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MEMOIRS
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SAN DIEGO SOCIETY OF NATURAL HISTORY
Volume II
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THE GEOLOGY AND PALEONTOLOGY OF THE MARINE PLIOCENE OF SAN DIEGO, CALIFORNIA
PART 1, GEOLOGY
BY
LEO GEORGE HERTLEIN
California Academy of Sciences AND
U. S. GRANT, IV University of California at Los Angeles
PUBLISHED WITH AID OF A GRANT FROM THE ELLEN BROWNING Scripps FOUNDATION
SAN DIEGO, CALIFORNIA PRINTED FOR THE SOCIETY Aucust 30, 1944
MEMOIRS
OF THE
SAN DIEGO SOCIETY OF NATURAL HISTORY
Volume II
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MEMOIRS
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SAN DIEGO SOCIETY OF NATURAL HISTORY
Volume II
THE GEOLOGY AND PALEONTOLOGY OF THE MARINE PLIOCENE OF SAN DIEGO, CALIFORNIA
PART 1, GEOLOGY
BY
LEO GEORGE HERTLEIN
California Academy of Sciences AND
U. S. GRANT, IV University of California at Los Angeles
PUBLISHED WITH AID OF A GRANT FROM THE
ELLEN BROWNING Scripps FOUNDATION
SAN DIEGO, CALIFORNIA PRINTED FOR THE SOCIETY Aucust 30, 1944
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Introduction
CONTENTS
~ Historical Review of the Literature of the San Diego Formation
Rhy stOera pny: anc 2 otc eng there
General Description ..... Climate and Rainfall . The Coastal Mesa Region The Terraces . ! San Diego Mesa Younger Terraces Older Terraces Shoreline Features... The Peninsular Mountains Stream Valleys and Drainage Coastal Mesa Region Peninsular Mountains Physiographic History General Relationships to Other Regions
Pre-Tertiary Igneous and Metamorphic Rocks
Cretaceous
Eocene
Absence of Oligocene and Miocene Rocks in the San Diego Region
Pliocene -
Distribution .
Lithology and Sedimentation
Pacific Beach and Soledad Mountain San Diego Mesa
Structure
Age and Correlation
The Sweitzer Formation
Origin of the Sweitzer Formation
Pleistocene .
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THE GEOLOGY AND PALEONTOLOGY OF THE MARINE PLIOCENE OF SAN DIEGO, CALIFORNIA
BY LEO GEORGE HERTLEIN AND U. S. GRANT, IV
PART 1, GEOLOGY INTRODUCTION
The chief object of this memoir is to describe and illustrate the marine Pliocene invertebrate fauna of the environs of San Diego,’ California. The present paper contains a geological introduction consisting of a review of the literature and a brief account, largely descriptive, of the general geological and physiographic features present in the region from which the fossils were obtained, including also some of the contiguous area north and east. No attempt has been made to prepare an exhaustive report on the geology and physiography of the region, but it is hoped enough has been given to form a geologic setting for the stratigraphic study and for a comprehension of some of the conditions which effected the deposition of the Pliocene sediments and the distribution and occurrence of the species enumerated later on.
The field work upon which the geologic and stratigraphic portions are based, and which has resulted in the accumulation of large collections of fossils, was begun in 1926 when the region was visited by Eric Knight Jordan and Hertlein. Some collections were made and notes taken but the work had hardly begun when it was interrupted by the lamentable death of Mr. Jordan. The present authors resumed field work in 1927 and 1928, and both of them, or one or the other, have made several later trips, particularly in 1937, to supplement the collections or obtain new information on the geology and stratigraphy. The laboratory work was done largely at the University of California at Los Angeles and at the California Academy of Sciences, although occasionally certain investigations were carried out at Stanford University, the University of California at Berkeley, and at the Museum of the San Diego Society of Natural History. The somewhat belated appearance of this paper is due in large part to the preoccupation of both authors with their other duties, the work having been done during such spare time as only occasionally became available.
It was originally planned to have the complete memoir issued at one time, but the limited and somewhat indefinite periods during which both the authors could devote their entire attention to bringing the manuscript up to date, and later reading the proofs, made its separation into parts necessary. The present part containing only the geological and general introductory matter will be followed by the several parts containing the systematic paleontology and it is proposed, in a final part, to include a discussion of the age and significance of the fauna as a whole and its correlation with that of other marine Pliocene formations in western North America.
Without the assistance of a number of persons this report could not have been prepared in its present form, and this occasion is taken to offer grateful acknowledgment of assistance received from them. Later special acknowledgment will be made of assistance received while working on the paleontologic parts. The late Mr. Frank Stephens, veteran naturalist of San Diego and former Curator Emeritus of the Museum of the San Diego Society of Natural History, was of great assistance to us during the field work. He accompanied us during the beginning of the field work and saved us much time in pointing out important fossil localities, some of which would have been difficult to discover or might have been overlooked entirely. Mrs. Kate Stephens of the same institution, now retired, assisted in a similar manner by calling attention to the occurrence of important species in certain parts of the region, and also prepared for us a large list of Pleistocene fossils from Spanish Bight. Mr. Eric Knight Jordan assisted during the initial stage of the field work, as related above.
' For an excellent compilation of the general facts concerning the history and features of San Diego, Calif., see, “San Diego, A California City”, Amer. Guide Series (sponsored and publ. by The San Diego Historical Society, San Diego, Calif.), x + 138 pp., frontispiece, 25 illustrations, 6 maps, 1937.
10 San Dreco Society oF Naturat History [Memotrs
Messrs. Frank B. Tolman and Ernest H. Quayle assisted us materially by collecting large faunas and pointing out some interesting geological features. Mr. Tolman gave helpful advice in regard to the Eocene stratigraphy, and Mr. Quayle has spent much time in assisting us with the illustrations. Dr. John E. Wolff, Professor of Geology Emeritus at Harvard University, prepared a short description of several crystalline rocks, and Dr. Gordon A. Macdonald, now of the U. S. Geological Survey, made some interesting petrographic and sedimentary studies for us. The Associated Oil Company permitted the use of well logs of this area which Mr. C. C. Church, paleontologist of that company, kindly examined for us. We here wish to acknowledge the cooperation of Mr. J. E. Pettijohn who kindly permitted us to examine the geologic reports of Mr. George H. Doane on the San Diego Gas and Petroleum Corporation’s Holderness No. 1 Well, which was drilled near the mouth of the Tia Juana River. Mr. Clinton G. Abbott, Director of the Museum of the San Diego Society of Natural History, permitted us to use all the facilities of that institution and cooperated in an important manner during the publication of the paper. Dr. G. Dallas Hanna of the Department of Paleontology, California Academy of Sciences, aided us many times with his valuable advice and cooperation. Both authors began this work while students of the late Dr. James Perrin Smith, Professor of Paleontology at Leland Stanford Jr. University, and they both remember his kind encouragement at that time. We wish to express our appreciation to Dr. Olaf P. Jenkins, Chief Geologist of the Division of Mines of the State of California, and to Mr. A. L. Ransome and Mr. E. Drew of the same department, for advice and assistance in the preparation of the geologic map and sections. Mr. F. P. Farquhar kindly furnished information regarding the construction of the first dike at San Diego by Derby. Secretarial work on the manuscript by Miss Winifred O’Neill is the result of work accomplished during a government Works Progress Administration Project No. 8569. The authors are grateful for the research grants from the University of California at Los Angeles received during the progress of this work.
HISTORICAL REVIEW OF THE LITERATURE
The sedimentary beds in the vicinity of San Diego have been mentioned or briefly described by many authors. Most of the early reports were brief notes based upon limited field observations or were mere descriptions of or references to some of the fossils that occur there. Tyson,” who made a short trip to San Diego about 1850, mentioned “that sedimentary rocks prevailed on the hills near the sea, and that there was an extensive diffusion of diluvial drift.” T. A. Conrad’s description’ of Ostrea vespertina from “near San Diego, California,” seems to have been the first paleontologic notice of the fossiliferous sedimentary beds in that region. In this paper, he referred the beds containing this Pliocene oyster questionably to the Miocene and in three later papers* he also considered these beds to belong to the Miocene. In 1856, William P. Blake,’ a pioneer geologist of the West, referred briefly to the general features of the region about San Diego and included with his report a small scale geologic map of southern California. He also mentioned certain fossils which he believed to be of Miocene age but which are now known to be of Eocene age. In two subsequent papers he likewise mentioned Tertiary fossils, probably the Eocene fossils which occur plentifully near the older part of the City of San Diego, near the San Diego Mission, and at various other localities. The Tertiary beds in the vicinity of San Diego were also mentioned by Antisell.°
In connection with the survey of the United States-Mexican Boundary made about the middle of the last century, Emory’ made a limited study of the geology in the vicinity of San Diego and briefly described the seaward dipping sedimentary beds of “coarse sand, clay, or marl, with occasional beds
2 Tyson, P. T., “Geology and Industrial Resources of California,” Senate Executive Document 47, 31st Congress, Ist Session,
1850 (reprinted with an introduction, published by Wm. Minifie and Co., Baltimore, 1851), p. 20. See also Lieut. E.O.C. Ord, p. 123.
> Conrad, T. A., Journ. Acad, Nat. Sci. Philadelphia, Ser. 2, Vol. 2, p. 300, 1854.
4 Conrad, T. A., House Document 129, Projected Vol. 3, 33rd Congress, Ist Session, 1855, pp. 11-18. U. S. Pac. R. R Repts., Vol. 5, pp. 322-327, 1856-1857. — Rept. U. S. Boundary Surv., Vol. 1, pt. 2, p. 160, 1857.
5 Blake, W. P., Senate Ex. Doc. 22, 34th Congress, Ist Session, Rept. Supt. Coast Surv., pp. 395-396, Map 60, 1855 (issued 1856). Proc. Amer. Assoc. Adv. Sci., Vol. 9, p. 224, 1856. U. S. Pac. R. R. Repts., Vol. 5, pp. 176-177, 1857.
6 Antisell, T., U. S. Pac. R. R. Repts., Vol. 7, p. 119, 1856. 7 Emory, W. H., Rept. of U. S, Boundary Surv., Vol. 1, pt. 2, p. 85, 1857.
VotumE IT] MarINE PLIOCENE OF SAN DrkEGO, CALIFORNIA 11
of interstratified pebbles” and noted particularly a thirty foot fossiliferous layer exposed in the steep bluffs which bound the lower part of the river valley at San Diego. This layer may have been the fossiliferous Eocene exposed on the sides of San Diego River Valley though on the south side the overlying Pliocene is likewise fossiliferous. This may be said to have ended the period of pioneer geological work during which much important information of a reconnaissance nature of various parts of California was obtained, largely in connection with the expeditions sent out by the War Department to make surveys for proposed railroad routes in what was then referred to as the “far West.”
Years later, after the business district of San Diego had moved from its former position (now called “Old Town”), near the mouth of San Diego River Valley,* to a position several miles south on the shore of San Diego Bay, a well was dug in the bottom of a small canyon back of the City in order to obtain water to supplement the meager supply for the small but rapidly growing settlement. This well, which was in City Park (now Balboa Park), penetrated a fossiliferous fine-grained sandstone from which Henry Hemphill, an early local conchologist, obtained a considerable collection of fossil shells. Part of this collection was sent to the late W. H. Dall who published a paper? in 1874 in which he discussed the “San Diego beds” and listed 51 definitely identified species and eighteen additional not specifically identified forms. He made the following comment as to the geologic age:
“The age of the deposit, in general terms, may be taken as Pliocene; though it is evident that the different epochs of the Tertiary are not as sharply separated on this coast as in some other parts of the world.”
A few years later Dall’® again listed the fauna from the San Diego well and added the descriptions of six new species. He noted Hemphill’s suggestion of the equivalence of the beds in the well from which the fossils were obtained, to the fossiliferous beds at Pacific Beach several miles to the northwest. Dall again gave the age as Pliocene.
In 1886 a note in the West American Scientist,'' presumably by its editor, C. R. Orcutt, stated :
“The peninsula in front of San Diego city is being improved by a company who propose making it a popular resort and to which the name Coronado Beach has been applied. In boring for Artesian water, a strata [stratum] of sand was found containing numerous fossil shells of the later tertiaries. The most prevalent species were Phasianella compta, Ostrea lurida and Anomia lampe in the order named. The strata was found at a depth of nearly seventy feet.” This occurrence was mentioned by Ellis,'* who stated that W. A. English regarded the three species as belonging to the lower Pliocene. However Tricolia compta Gould is not definitely known below the Pleistocene and the other two species are much more common in the Pleistocene than in the Pliocene, hence it is almost certain that the beds encountered in this well are of Pleistocene age.
In a catalogue of California fossils, published in 1888, ]. G. Cooper'’ listed numerous species from the Pliocene of San Diego, some of them being reported for the first time in those beds. In the same year Goodyear’ discussed the geology of San Diego County in which paper the following statement occurs :
“Commencing at the Mexican boundary line, the Mesa formation, of pleiocene age, is some ten or twelve miles wide, and from thence it forms an uninterrupted belt of varying width for a distance of more than fifty miles along the coast towards the northwest, or as far as the Santa Margarita River.” It is apparent that Goodyear included beds other than the Pliocene, for most of the mesa north of
‘i 8 Often known as Mission Valley but not to be confused with a Mission Valley further north in the San Luis Rey River Valley.
9 Dall, W. H., Proc. Calif. Acad. Sci., Vol. 5, pp. 296-299, 1874. According to Henry Hemphill, the collector, the fossils were obtained from the well at a depth between 140 and 160 feet. The matrix was said to be hardly consolidated in some
parts and quite hard in others. The occurrence of these fossils was first mentioned by R. E. C. Stearns (Proc. Calif. Acad. Sci., Vol. 5, no. 10, pp. 153-55, Oct., 1873).
10 Dall, W. H., Proc. U. S. Nat. Mus., Vol. 1, pp. 10-16, 26-30, 1878. 11 Orcutt, C. R., West Amer. Scientist, Vol. 2, no. 15, p. 32, 1886. 12 Ellis, A. J., in Ellis, A. J., and Lee, C. H., U. S. Geol. Surv., Water Supply Paper 446, p. 64, 1919.
'3 Cooper, J. G., Calif. State Mining Bureau, 7th Ann. Rept. State Mineralogist, pp. 223-308, 1888. Parts 2, 3, 4 and 5 of this catalogue appeared as Bulletin 4, Calif. State Mining Bureau, 65 pp., 6 pls., 1894.
14 Goodyear, W. A., Calif. State Mining Bureau, 8th Ann, Rept. State Mineralogist, p. 522, 1888.
12 San Disco Socrety oF Naturat History (Memoirs
San Diego River Valley is of Eocene age.
In 1889 Orcutt!’ published a list of Tertiary fossils from localities such as Pacific Beach, False Bay (now called Mission Bay), Ocean Beach and Roseville, but he added nothing new on correlations. Some of the localities are probably Pleistocene. At Pacific Beach Orcutt noted three imperfectly defined members. The oldest he stated was.a sandstone with moulds of various bivalves and imperfect valves slightly resembling oysters; the second, distinctly softer beds, containing Opalia, Janira, Pecten, Terebratula?; the third, younger beds more recent in character, containing most of the other species. Probably his oldest bed was Eocene, the second Pliocene, and the third either Pliocene or Pleistocene.
A number of the West American Scientist for 1900 (Vol. 10, no. 4, whole no. 86, pp. 17-19), contains a discussion of the geology of the San Diego region by H. W. Fairbanks. Some of the structural features are mentioned and particular mention is made of the changes in elevation which took place in the late Tertiary and Quaternary. Fairbanks mentioned a “Mesa formation” which no doubt included the Pliocene beds. This discussion in the West American Scientist appears to be a quotation from the San Diego Sun of April 16, 1891.
A paper on correlation by Dall and Harris'® was published in 1892, in which they gave a brief review of the existing literature concerning the San Diego region and quoted Dall’s original determination of the Pliocene age of the fossils from the San Diego well.
At this time some of Fairbanks’ geological work for the California State Mining Bureau was being published. In one paper’” he discussed the geology in the vicinity of San Diego and referred to strata of Quaternary, Pliocene and questionably Miocene age. He gave a good outline description of the basin in which the San Diego beds were deposited and stated that apparently Point Loma and the Soledad Hills formed the western and the northern margins of the basin. He also pointed out that a recent uplift had taken place along the ocean side of the mesa. In a second paper'® he stated:
“The Miocene is not positively recognized near San Diego, but the mesas along the eastern side of the bay on which the city is situated are filled with Pliocene fossils; the strata being separated from the Chico-Tejon by a small non-conformity.”
In 1893 an important paper’? on the post-Pliocene diastrophism of the coast of southern California by A. C. Lawson was published. This paper contains an excellent description and discussion of the marine terraces in the San Diego region. Lawson believed the San Diego beds to be in part a portion of a delta of Pliocene age, the age determination being based upon a comparison with Miocene strata elsewhere and upon Dall’s paleontologic evidence. .
A number of later papers have contained indirect references to the San Diego beds in connection with correlations of other deposits on the Pacific coast. Among these may be mentioned papers by Dall,?° Arnold,”' Rivers,” J. P. Smith,’* Louderback,** Merrill”? Clark and Twitchell,*° Moody,””
15 Orcutt, C. R., West Amer. Scientist, Vol. 6, whole no. 45, pp. 70-71, 1889.
16 Dall, W. Hi, and Harris, G. D., U. S. Geol. Surv., Bull. 84, p. 216, 1892.
17 Fairbanks, H. W., Calif. State Mining Bureau, 11th Ann. Rept. State Mineralogist, 1891-1892, pp. 96-97, 1 map, 1893.
18 Fairbanks, H. W., Amer. Journ. Sci., Ser. 3, Vol. 45, p. 477, 1893. A year later Cooper stated that the fossils found by Fairbanks indicated that the whole mesa was of Pliocene age. See Calif. State Mining Bureau, Bull. 4, p. 52, 1894.
19 Lawson, A. C., Univ. Calif. Publ. Bull. Dept. Geol., Vol. 1, pp. 115-160, pls. 8, 9, Dec., 1893. See page 119
20 Dall, W. H., U. S. Geol. Sury., 17th Ann. Rept., pt. 1, p. 476, 1895. In this paper Dall reported fossils collected by Diller in northwestern Oregon, stating that some of them belonged to “‘the Pliocene (horizon of Pacific Beach, San Diego, Cal.).”
21 Arnold, R., Mem. Calif. Acad. Sci., Vol. 3, pp. 13, 57-64, 1903. — U. S. Geol. Surv., Prof. Paper 47, p. 28, 1906.
22 Rivers, J. J., Bull. Southern Calif. Acad. Sci., Vol. 3, no. 5, p. 69, 1904. Rivers mentioned sandstones in the Santa Monica Mountains which he believed represented the San Diego Pliocene in that area.
23 Smith, J. P., Proc. Calif. Acad. Sci., Ser. 4, Vol. 9, no. 4, pp. 149, 151, 1919.
24 Louderback, G. D., Univ. Calif. Publ. Bull. Dept. Geol., Vol. 7, no. 10, p. 223, 1913. This paper contains a correlation table of west coast Tertiary formations, in which the San Diego formation is considered equivalent to the Purisima formation of central California, since reference is made to “Sandstones of San Diego and Half Moon Bay with Pecten healeyi.” Trans. San Diego Soc. Nat. Hist., Vol. 2, no. 3, pp. 87-97, 1916.
25 Merrill, G. P., Calif. State Mining Bureau, 14th Ann. Rept., pt. 5, pp. 639-644, 1916. Issued as a separate, Dec., 1914. Contains a correlation table and discussion of the geology of the San Diego region.
26 Clark, W. B., and Twitchell, M. W., U. S. Geol. Surv., Monograph 54, p. 102, 1915. In a correlation table the San Diego formation is placed below the Merced and given as equivalent to the Caloosahatchee and Nashua of the eastern Gulf area, and the Waccamaw of the south and middle Atlantic border.
27 Moody, C. L., Univ. Calif. Publ. Bull. Dept. Geol., Vol. 10, no. 4, p. 50, 1916
VotuME II] MarINE PLIOCENE OF SAN D1EGo, CALIFORNIA 13
B. L. Clark,?* Kew,2’ Carson,’ Hertlein,’’ E. K. Jordan and Hertlein,*? Waterfall,’* Pressler,* Woodring,” Soper and Grant,*° Reed,” and others.”®
In an important correlation paper Dall” stated that the Pliocene marls in the San Diego well also occur below the Pleistocene beds at Pacific Beach, along the shores of False Bay and on the Coronado Peninsula. He stated that the horizon could be recognized at various other localities to the north, including Deadman Island, Harbor Hill, San Pedro, and also at Todos Santos Bay, Lower California. In the correlation table Dall placed the San Diego beds below the Merced group and indicated them to be equivalent to the Caloosahatchee beds of the Gulf States and to the Waccamaw beds of the Atlantic coast. The latter he considered in general correlative with the Crag beds of England. A few years later*® he remarked that the only known strictly defined Pliocene marine fauna of California was that at San Diego. He called attention to the difference between the Pliocene and Recent faunas of San Diego, and the Pliocene and Recent faunas of northern California and Oregon, many of the San Diego Pliocene species being known in the living fauna only in the Gulf of California.
Ralph Arnold‘! appears to have been the first to use the name “San Diego Formation” for the Pliocene strata at San Diego. In his important memoir** on the paleontology and stratigraphy of the San Pedro region he included the results of his collecting and geological field work in the San Diego district, including faunal lists of species obtained from several Pliocene and Pleistocene localities— lists which have been used with little additions or alterations by later writers almost up to the present time. In a series of important later papers® incorporating the results of his work for the U. S. Geological Survey he republished the faunal lists of species occurring at San Diego, described new species from there, or made correlations which mentioned equivalents of the San Diego formation in other parts of California. Some of his opinions on correlations will be briefly summarized here. In 1906 he considered the lower part of the San Diego formation to be equivalent to the middle and upper part of the Purisima formation, and the upper part of the San Diego formation equivalent to the Merced. In 1907 he considered the Third Street Tunnel (Los Angeles) and Temescal Canyon (near Santa Monica) faunas to be of “San Diego” age. In. several papers he referred to the middle
28 Clark, B. L., Journ. Geol., Vol. 29, p. 610, 1921. — Proc. First Sci. Confer. Pan-Pacific Union, pt. 3, Bernice P. Bishop Mus., Special Publ. 7, pt. 3, p. 817, 1921.
29 Kew, W. S. W., Bull. Amer. Assoc. Petrol. Geol., Vol. 7, pp. 419-420, 1923. The Saugus formation of the Ventura basin believed to be equivalent to the San Diego formation. U. S. Geol. Surv., Bull. 753, p. 89, 1924. Saugus and San Diego formations believed to be equivalent.
30 Carson, C. M., Pan-Amer. Geologist, Vol. 43, no. 4, pp. 265, 268, 1925. Contains a list of San Diego Pliocene fossils
31 Hertlein, L. G., Proc. Calif. Acad. Sci., Ser. 4, Vol. 14, no. 1, p. 6, 1925. Pliocene of Cedros Island, Lower California, Mexico, stated to be in general equivalent to the San Diego Pliocene of Pacific Beach.
32 Jordan, E. K., and Hertlein, L. G., Proc. Calif. Acad. Sci., Ser. 4, Vol. 15, no. 14, pp. 422-423, 1926. Relationship between the Pliocene and Eocene at Pacific Beach clarified and Pliocene of San Diego, Turtle Bay and Cedros Island stated to represent approximately middle Pliocene or the lower part of the upper Pliocene.
33 Waterfall, L. M., Univ. Calif. Publ. Bull. Dept. Geol. Sci., Vol. 18, no. 3, pp. 80-81, April 6, 1929. Upper Pico fauna of Ventura County correlated with Pliocene of San Diego.
34 Pressler, E. D., Univ. Calif. Publ. Bull. Dept. Geol. Sci., Vol. 18, no. 13, p. 334, Sept. 30, 1929.
35 Woodring, W. P., Proc. Calif. Acad. Sci., Ser. 4, Vol. 19, no. 6, pp. 57-64, July 15, 1930. San Diego Pliocene equivalent noted north of Simi Valley.
36 Soper, E. K., and Grant, 1v, U. S., Bull. Geol. Soc. Amer., Vol. 43, p. 1041-1068, Dec., 1932. See pp. 1066-1067 San Diego Pliocene considered in part equivalent to the Third Street Tunnel beds of Los Angeles, and also in part equivalent <o the Pliocene of Elsmere Canyon.
37 Reed, R. D., “Geology of California.” Published by Amer. Assoc. Petrol. Geol., Tulsa, Oklahoma, May, 1933. See pp. 227-228. This important work on the geology of California contains a brief discussion of the San Diego formation.
38 A number of very brief references to the Pliocene of San Diego occur in the literature but need not be included here, since little new information is contained in them.
39 Dall, W. H., U. S. Geol. Surv., 18th Ann. Rept., pt. 2, opp. p. 334, p. 337, 1898
40 Dall, W. H., in Diller, J. S., U. S. Geol. Sury., Bull. 196, pp. 37-39, 1902.
41 Arnold, R., Journ. Geol., Vol. 10, p. 130, 1902.
42'Arnold, R., Mem. Calif. Acad. Sci., Vol. 3, pp. 13, 57-59, 1903.
43 Arnold, R., U. S. Geol. Surv., Prof. Paper 47, p. 28, 1906. — Proc. U. S. Nat. Mus., Vol. 32, pp. 527, 544, June, 1907
~ In Eldridge, G. H., and Arnold, R., U. S. Geol. Surv., Bull. 309, pp. 23-24, Oct. 23, 1907. — Smithson. Miscell. Coll., Vol 50, pp. 431, 445, Dec. 13, 1907. — In Arnold, R., and Anderson, R. V., U. S. Geol. Surv., Bull. 322, pp. 148, 152, 154, Jan. 4, 1908. — Proc. U. S. Nat. Mus., Vol. 34, pp. 384-385, Aug. 8, 1908. — Journ. Geol., Vol. 17, no. 6, opp. p. 532, 1909. - U.S. Geol. Surv., Bull. 396, pp. 9, 48, 1909. — In Arnold, R., and Anderson, R. V., U. S. Geol. Surv., Bull. 398, p. 48. 1910. — The correlation table in this paper was also cited by B. Willis in U. S. Geol. Surv., Prof. Paper 71, p. 818, 1912.
14 San Disco Society OF Naturat History {Memoirs
Fernando fauna of the Ventura basin as probably equivalent to the lower part of the San Diego formation and recognized Pliocene beds of San Diego age, or approximately San Diego age, or containing species occurring in the San Diego Pliocene and suggestive of similar age, in the Santa Monica region and in other basins. In 1908 Arnold listed “A gasoma stanfordensis” questionably from the San Diego formation on Mission Grade, near the head of Sixth Street, San Diego. The Agasoma- like species which occurs at that locality is a Trophosycon™ in the lower part of the Pliocene beds. In general, Arnold’s correlations have been but little changed by subsequent work.
Aguilera’ in 1906 mentioned a formation at Tijuana, Lower California, Mexico, which he stated was the equivalent of the Purisima of California and which he considered to belong at the base of the Pliocene. This no doubt referred to the southern extension of the San Diego formation on the south side of the International Boundary.
In 1910 J. P. Smith*® placed the San Diego formation in the lower Pliocene and correlated it with the middle Fernando of Los Angeles, Ventura, and Santa Barbara Counties, lower and middle part of the Tulare formation of the San Joaquin Valley, lower and middle part of the Paso Robles formation at the type section in Salinas Valley, upper part of the Purisima at Half Moon Bay, and middle part of the Berkeleyan of the Mount Diablo region.
In his later classic paper on the climatic relations of the Tertiary and Quaternary faunas of the California region, Smith” gave a list of fossil mollusks from the San Diego formation and discussed the climatic and stratigraphic relations of the fauna to other marine Pliocene faunas of California. He correlated the San Diego Pliocene with the Merced of Seven Mile Beach (just south of San Francisco) and considered it to be the southern equivalent of that series. He also stated, following Dall, that this zone is found in the region of Todos Santos Bay, Lower California. However, beds of that age have not been reported from near Todos Santos Bay by later workers. It is not known what the original basis of this age determination may have been. Smith considered the fauna from the City of Los Angeles described by Moody** to be of the same age as that of the San Diego Pliocene, but it is now believed that Moody’s fauna is later in age than that of the San Diego formation.” According to Smith the European equivalents of the San Diego and Merced are the Red Crag of England, Scaldisian of Belgium, and Astian of Italy.
In a paper’ on the geology and ground waters of the western part of San Diego County, Ellis included considerable information on the physiography and stratigraphy of the San Diego Tertiary basin. The geological map is of considerable interest but the boundary of the Pliocene formation is inaccurate as it includes considerable Eocene north of San Diego River Valley and probably some Pleistocene elsewhere.
Marcus A. Hanna’s report”' on the geology of the La Jolla Quadrangle, an area consisting largely of Eocene strata, contains a short but significant discussion of the Pliocene beds occurring in small areas in the southern part of that Quadrangle. Hanna mapped the Pliocene-Eocene contact with considerable accuracy and thus removed much Eocene from the area now known to be occupied by the San Diego formation, which had been incorrectly placed there by others due to scarcity of fossils and lack of sufficient field work.
Hertlein”’ in 1929 completed a thesis which was submitted to the Leland Stanford Jr. University,
44 The lower part of the Pliocene as exposed at Elsmere Canyon contains a fossiliferous zone which includes Trophosycon. This fossil zone is within 100 feet stratigraphically above the Pliocene-Eocene contact. This affords a striking similarity to the Pliocene beds at San Diego.
45 Aguilera, J. G., Cong. Geol. International, 10th Session, Mexico, 1906, Vol. 10, fasc. 1, pt. 6, p. 244, 1907.
46 Smith, J. P., Journ. Geol., Vol. 18, no. 3, opp. pp. 217 and 226, 1910.
47 Smith, J. P., Proc. Calif. Acad. Sci., Ser. 4, Vol. 9, no. 4, pp. 150-152, 1919, See also, Calif. State Mining Bureau, Bull. 72, table opp. p. 16, p. 38, 1916.
48 Moody, C. L., Univ. Calif. Publ. Bull. Dept. Geol., Vol. 10, no. 4, pp. 39-62, pls. 1, 2, 1916.
49 This correlation was recently discussed by Soper, E, K., and Grant, 1v, U. S., Bull. Geol. Soc. Amer., Vol. 43, pp. 1041-1068, 1932.
50 Ellis, A. J., in Ellis, A. J., and Lee, C. H., U. S. Geol. Surv., Water Supply Paper 446, pp. 56-68, 1919 5) Hanna, M. A., Univ. Calif. Publ. Bull. Dept. Geol. Sci., Vol. 16, no. 7, pp. 216-218, 1926.
52 Hertlein, L. G., “The Geology and Paleontology of the Pliocene of San Diego, California,” a thesis presented to the Department of Geology of Leland Stanford Junior University in partial fulfillment of the requirements for the degree of Doctor of Philosophy, 1929. — Stanford Univ. Bull., 5th Ser., Vol. 4, no. 78, pp. 81-85, July 31, 1929.
VotumE IT} MarINE PLIOCENE OF SAN DIEGO, CALIFORNIA 15
entitled “The Geology and Paleontology of the Pliocene of San Diego, California,” and an abstract of this was published the same year. He concluded that the San Diego Pliocene could be correlated with the Pliocene of Elsmere, Holser, and Pico Canyons, which he considered to be lower Pliocene in age. The Pliocene fauna at Cedros Island and Turtle Bay in Lower California was said to be the closest equivalent to the south.
Grant and Gale, in their memoir on the Pliocene and Pleistocene Mollusca of California, reported many species from the San Diego formation, and Gale” gave a discussion of the stratigraphy of the San Diego basin based mostly on field data furnished by Grant. A geologic map”* of California prepared under the direction of Dr. Olaf P. Jenkins was published in 1938. The geology of the San Diego region on this map is essentially as it appears in the unpublished thesis of Hertlein. A brief summary of some of the salient features of the geology of the area included in the present paper, with numerous well records, was published by the present authors” in a recent number of the California Journal of Mines and Geology.
A number of papers* not mentioned above contain brief references to the San Diego Pliocene, but generally they merely restate the conclusions or opinions of others. A few contain descriptions of new or supposedly new San Diego Pliocene fossils, but these latter will be included in the references under the particular species in the systematic part of the present work.
The name San Diego formation has been used by Meyerhoff’® for upper Cretaceous beds in the West Indies. That formational name has had many years prior use in California, and it would appear to be advisable to rename Meyerhoff’s formation in order to avoid possible confusion.
PHYSIOGRAPHY GENERAL DESCRIPTION
The area considered in this report can be divided physiographically into two parts, the coastal mesa region on the west and the mountainous region on the east. These two parts are very distinct, both in their topography and their geology, the boundary between them being both a topographic and a geologic unconformity (see physiographic block diagram). Each part has had a somewhat different history and each is comprised of different rocks. They will be considered separately, although a complete physiographic picture of the whole area can be obtained only by an understanding of the genetic connection which exists between them. Some of the features of the coastal mesa region have been derived from the region to the east, and both, to some extent, have been influenced by the same forces and geologic processes. The climate, particularly the rainfall, has been of importance in determining the present relief features of both regions, hence it seems well to present a brief and general description of the climate at the beginning of this discussion.
CLIMATE AND RAINFALL
The climate of the San Diegan region varies considerably with elevation above sea level and distance from the coast. Statistics may be obtained from official government weather reports, so that here it will be necessary only to give such general facts as might have a bearing upon weathering
53 Gale, H. R., in Grant, 1v, U. S., and Gale, H. R., Mem. San Diego Soc. Nat. Hist., Vol. 1, pp. 45-49, 1931.
4 54 State of Calif., Dept. Nat. Resources, Division of Mines. Geologic Map of Calif., prepared by Olaf P. Jenkins. _ 1, 1938.
> Hertlein, L. G., and Grant, 1v, U. S., “Geology and Oil Possibilities of Southwestern San Diego County,” Calif. Journ. Mines and Geol., Vol. 35, no. 1, 35th Rept. Calif. State Mineralogist, pp. 57-78, 8 figs. in text, Jan., 1939 [received at library of the California Academy of Sciences Aug. 23, 1939].
* After the present paper was submitted for publication, a paper by W. P. Woodring, R. B. Stewart, and R. W. Richards appeared, entitled “Geology of the Kettleman Hills Oil Field, California,’ Prof. Paper 195, U. S. Geol. Survey, 1940 [issued June 7, 1941]. A brief discussion of the fauna of the Pliocene of San Diego is given on pp. 112-113. See also correlation table opp. p. 112. See also correlation chart by U. S. Grant, 1v, and L. G. Hertlein, State of Calif. Dept. Nat. Resources, Div. Mines, Bull. 118, preprint of pt. 2, p. 202, Aug. 1941 (issued Sept. 11, 1941); also preprint of pt. 3, pp. 367-369, 1 text fig., March, 1943 (issued July 1, 1943).
56 Meyerhoff, H. A., Science, New Ser., Vol. 71, no. 1838, p. 323, 1930. Also, New York Acad. Sci., Sci. Sury. Porto Rico and the Virgin Islands, Vol. 2, pt. 3, pp. 289-290, 1931. The type locality of the San Diego formation is at Punta San Diego, Porto Rico, Upper Cretaceous.
16 San Dieco Society oF NaturaL History [Memoirs
and the other processes of erosion.” The coastal region has an equable temperate dry climate with moderate precipitation occurring chiefly between the months of October and April.”* At San Diego the average annual rainfall is about ten inches. All of the mesa region described in this report is within this coastal belt of semi-aridity. The higher mountains of central and eastern San Diego County have a heavier rainfall and a much less equable climate, with a noticeably greater diurnal and seasonal range of temperature. The coastal belt rarely experiences freezing temperatures in winter nor oppressively hot days in summer, but the higher mountains to the east frequently receive a few inches of snowfall during winter, and during summer the temperature, in some of the valleys, occasionally reaches 100°F. The higher ridges and peaks act as a trap for the eastward drifting rainstorms and a precipitation of over 40 inches per year occurs on the western slopes of such mountains as the Cuyamacas and Palomar.”? A rainfall of over twenty inches per year occurs throughout a north-south belt within the heart of the higher elevations. Lee® has assembled considerable data on precipitation in San Diego County®' to which the reader is referred for more information than seems justifiable to be included here.
THE COASTAL MESA REGION
The coastal mesa region extends north and south, parallel and adjacent to the coast line throughout the San Diego area and continues many miles beyond its northern and southern limit. On the west this mesa region is truncated by shoreline processes where it extends to the beach, or breaks off more gradually in a series of marine terraces where separated by bay or coastal plain from the present sea. The coastal plain is of such limited extent that it is considered a minor subdivision of the mesa region. In width this region varies from about 6 to 14 miles and in height from over 800 feet (the summit of Soledad Mountain) to near sea level; but the nearly flat-topped, slightly dissected mesa that forms the most conspicuous feature has an elevation ranging from about 300 to 550 feet.
The coast line within the area considered here is modified by two promontories, the broad northern
57 The climate has not only directly influenced the more important erosive processes but has determined the type of vegetation. This has had, in turn, a bearing on the physiographic processes. Lichens, ordinarily such inconspicuous plants, here form an al- most continuous protective mat over parts of the mesa region, and appear to greatly retard rain wash and sheet-flood erosion, prevent the rapid development of gullies, and thereby facilitate the accumulation of soil and déeply weathered mantle rock. For example, on the mesa east of Paradise Valley and north of the Sweetwater River Valley a lichen-moss cover is very prominent. Specimens collected early in 1938 were submitted to Professor Carl Epling of the Department of Botany, University of California at Los Angeles, who identified the flora as follows: “The vegetative part of a moss thus far undeterminable; a fern, Selaginella cinerascens; and two lichens, Parmelia conspera variety stenophylla and Urceolaria scruposa.’’ This vegetative mat holds the surface of the soil firmly in place, delays sheet-flood run-off, and by lessening the turbidity of run-off, facilitates percolation of rain water into the soil. A decrease in mud content has been shown to have an important bearing on infiltration of water into the soil. See: Loudermilk, W. C., “Further studies of factors affecting surficial run-off and erosion,’ Proc. Internat. Congr. Forestry Exper. Stations, 1929, pp. 606-628, 14 figures. Reviewed by Kirk Bryan in Zeitschrift fiir Geomorphologie, Vol. 6, 1931.
58 From 1908 to 1933 about 95% of the annual rainfall at San Diego occurred between October and April inclusive and almost 74% between December and March inclusive. (See State of California, Dept. Public Works, Publ. Division of Water Resources, Bull. 48, table 3, 1935. This paper contains considerable information on rainfall, run-off, and water resources in general of San Diego County). R. J. Russell, in his studies of climate, using the system of W. Képpen (Grundriss der Klimakunde, Berlin and Leipzig, 1931) and the Képpen-Geiger Klimakarte der Erde (Gotha, Justus Perthes, 1928), classified the climate in the San Diego coastal region as BWhn and the foothills as BSh. The BWhn climate is essentially an arid, foggy, coastal desert, and the BSh its an arid steppe type. (See Russell, R. J., “Dry Climates of the United States. 1. Climatic Map,” Univ. Calif. Publ. Geography, Vol. 5, no. 1, pp. 1-41, pl. 1, 8 text figs. Jan. 13, 1931. See especially p. 39, and pl. 1). These two climates continue along the west coast of Lower California, Mexico, with variable width, to below 31° North Latitude. (See Meigs, 3rd, Peveril, “The Dominican Mission Frontier of Lower California,” Univ. California Publ. Geography, Vol. 7, pp. 1-232, Nov. 30, 1935. See especially fig. 3 and p, 15). Both these climates occur in Nelson’s Upper Sonoran Life-zone in Lower California. (See Mem. Nat. Acad. Sci., Vol. 16, Mem. 1, pl. 32, 1922 [separate dated 1921}).
>9Hor Springs Mt., northeast of Warner’s Hot Springs, has the two highest peaks in San Diego County, namely Black Rabbit Peak, 6,633 feet, and Hot Springs Peak, 6,535 feet, which are separated by a short saddle. The only other point over 6,500 feet high is Cuyamaca South Peak, 6,527 feet. There are probably a dozen additional peaks in the County with an elevation of 6,000 feet or more. Some of the better known are Laguna Peak, 6,375; Monument Peak, 6,321; San Ysidro Mt., 6,147; Palomar Mt., 6,138; and Cuyamaca North Peak, 6,030. (Information received from Mr. B. B. Moore in the office of E. R. Childs, San Diego County Surveyor; Mr. George Buxton, acting for N. J. Farrell, Forest Supervisor, Cleveland National Forest, United States Department of Agriculture; and Mr, L. W. Deewall, San Diego County Planning Engineer. February and March, 1943).
60 Lee, C. H., in Ellis, A. J., and Lee, C. H., U. S. Geol. Surv., Water Supply Paper 446, pp. 76-99, with several tables and plates, 1919. See also, Calif. Div. Water Resources Publ., Bull. 48, 1935.
61 Instrumental records of annual precipitation at San Diego began with the season 1850-1851. An interesting study of earlier rainfall fluctuations in southern California has been published by the Metropolitan Water District of Southern California. See Lynch, H. B., “Rainfall and Stream Run-off in Southern California since 1769,” Los Angeles, Calif., Aug., 1931.
VotumE II] MarINE PLIOCENE OF SAN D1EGO, CALIFORNIA 17
one formed by the mass of Soledad Mountain near La Jolla, the southern one formed by the isolated north and south trending Point Loma, and two bays, shallow Mission Bay (formerly called False Bay) between Soledad Mountain and Point Loma, and the larger and deeper San Diego Bay, which is protected by Point Loma and a long sand spit called the Silver Strand, Coronado and North Island. The details of coastline contour can be readily seen on the map (page 50) or on the physiographic block diagram. The latter also shows the San Diego Mesa and other relief features in the region.
The eastern boundary of the mesa region is determined by the contact of the overlapping edge of the Tertiary (Eocene or Pliocene) sediments upon the older crystalline rocks that form the foothills of the mountainous region to the east. This boundary line becomes somewhat indefinite in detail where the feather edge of the eastward thinning Tertiaries becomes a mere veneer of soil resting upon
the older rocks beneath.
THE TERRACES San Diego Mesa
The most conspicuous topographic feature of the coastal portion of the San Diego region is the broad, relatively flat mesa which occupies most of the area included in the San Diego and La Jolla Quadrangles. This mesa, here referred to as the San Diego Mesa, is but one of several marine terraces or plains of marine denudation and deposition, the higher ones, of greater age, being considerably dissected and less noticeable, the lower ones, developed on the western margin of the mesa, being of relatively slight area though readily seen where not removed by later erosion.
The San Diego Mesa, the principal terrace, is physiographically a unit, though its separation by the larger stream valleys has resulted in different names being applied to different parts (see Plate 3). Thus the mesa south of Otay Valley is known as the Otay Mesa and the one north of San Diego River as the Linda Vista Mesa or Linda Vista Terrace.** Both of these mesas were at one time continuous before stream erosion began the work of dissection. In the south this mesa has been elevated higher and apparently more rapidly than in the north, for near the Mexican Boundary (Otay Mesa) the surface is over 550 feet above sea level, whereas the western portion of the mesa just south of San Diego River Valley attains an elevation but little over 300 feet; and the greater vertical interval between the lower terraces in the south indicates a more rapid uplift there.
The surface of the San Diego Mesa, where unmodified by erosion subsequent to emergence and uplift, slopes gently toward the west except in the southern part, where Otay Mesa has either been tilted slightly eastward or its eastern surface lowered by erosion more than its western.” This mesa, when viewed from a point on its surface, appears almost like a featureless plain, the river valleys and canyons being below the line of vision. However, close inspection reveals some slight irregularities in detail, such as gentle undulations, long low ridges, some of which are believed to be beach ridges, and occasional areas of small hillocks or prairie mounds (Plate 6). The gentle undulations may be due in part to differences in rate of weathering and erosion or to irregularities of uplift, but generally the exposures of the underlying beds are inadequate to determine the cause. The hillocks, which are well developed on parts of the Linda Vista Terrace and the mesa west of Sweetwater Reservoir and the Otay Mesa, often attain a height of 3 or more feet and a basal diameter of 10 to 20 feet. Small ephemeral pools of water collect between them during spring rains. These prairie mounds or hillocks are not confined to the tops of the mesa but are sometimes distributed over its gentle marginal slopes into shallow broad swales which, in some cases, may represent stream valleys of an older cycle than the present one. It seems likely that their origin is connected with wind action and former vegetation, possibly the accumulation of aeolian sand around bushes, or irregular deflation between them. The
62 Ellis, A. J., in Ellis, A. J., and Lee, C. H., U. S. Geol. Surv., Water Supply Paper 446, pp. 27-28, pl. 7, 1919. This paper contains an interesting description of the physiography of western San Diego County. See pp. 20-50.
63 We did not observe any eastward dip of the strata underlying the Otay Mesa which could be relied upon as significant. A one degree eastward dip on the north side of Sweetwater Valley near its mouth is probably local. The eastward slope of the surface appears to be due to erosion.
18 San Dieco Society oF Naturat History [Memoirs
abundance of these mounds suggests a rather widespread condition different from the present,” possibly a superabundance of loose sand or finer-grained material exposed to wind transportation soon after the sea regressed from the present mesa top and while it was actively cutting rapidly widening benches at slightly lower levels, which are now represented by the terrace 50 feet below the top of the Otay Terrace and the lower ones mentioned by Ellis. The rather uniform distribution of these mounds would suggest the even distribution of former vegetation as a controlling factor. An examination of the soil map of this area” might lead one to suspect that the prairie mounds were connected in some way with the type and degree of weathering of the soil series on which they are formed. For example, they are common on strongly or maturely developed secondary soils such as the Olivenhain series, the Las Flores loamy fine sand and the Redding series, which have been mapped in the mesa lands of western San Diego County. These soils have an acidic uppermost layer, a clay or hardpan subsoil, and occur on elevated terraces both north and south of the City of San Diego where prairie mounds also occur. Such soils promote the growth of widely spaced bushes or clumps of vegetation and in that indirect way control the spacing of mounds of aeolian material around plants.°° The fact that lag-gravel does not show notable concentration in the intermound areas may not be especially significant, as mounds of sand gathered by the wind around clumps of bushes on the Antelope Valley east of Palmdale have numerous pebbles on them where they were exposed by burrowing animals now living in holes under the bunches of shrubbery. (See Dalquest and Scheffer, Journ. Geology, Vol. 50, no. 1, p. 68, Jan.-Feb., 1942).
The beach ridges, described by A. J. Ellis in the paper already referred to (1919, p. 30), are quite conspicuous in the region north of the San Diego River (well shown on the topographic map of the La Jolla Quadrangle) where they have controlled the plan of subsequent canyon development, forcing Tecolote Canyon and smaller canyons east of La Jolla to assume a partial trellis drainage
64 Kirk Bryan has expressed the opinion that the ‘work of the wind is effective only where the rainfall is less than 10 inches per year (Amer. Journ. Sci., Ser. 5, Vol. 6, p. 306, 1923). The San Diego prairie mounds probably originated during a drier epoch preceding the Recent epoch.
65 Storie, R. E., and Carpenter, E. J., “Soil Survey of the El Cajon Area, California,’ U. S. Dept. Agric., Ser. 1930, no. 15, 1930. For a soil map of the northwestern part of San Diego County see the pamphlet and map by the same authors in “Soil Survey of the Oceanside Area, California,” U.S. Dept. Agric., Ser. 1929, no. 11, 1929.
66 A letter dated October 29, 1937, from Professor Chas. F. Shaw, Division of Soil Technology, College of Agriculture,
University of California, Berkeley, contains the following remarks on prairie mounds:
“TI have long been interested in these mounds and have studied them from time to time incidental to studies of other soil features. It is my opinion that they are in most locations due to the wind drifting of soil and its accumulation around scattered plants. In the deserts where creosote bush is the dominant vegetative form the plants are usually spaced many feet apart. Each plant has an accumulation of soil about its base forming a more or less definite mound. This accumulation about the plants usually goes on until the intervening area has been stripped to the point where a desert pavement has accumulated that retards or prevents further wind drifting of the soil. The removal of the vegetation usually results in the dissipation of the mounds by further wind erosion but when such areas are first cleared the location of the mounds is very striking. Such mounds are builded not only where the drifted material is sand but also where it is as heavy as clay. It appears that this is the probable cause of such mound formation and I believe that it explains the occurrence of the mounds on most of the soils. On some of the soils, however, there is evidence that such wide-spaced vegtation may have served to prevent water erosion and the mounds may be remnants of an older surface. This is the case on some of the soils of the Redding series in the northern part of the state.
“In regions such as the San Diego coastal plain, the deep soils without heavy accumulations of clay in the subsoil or the presence of hardpan horizons will usually bear a rather complete vegetative cover. Where, however, we have soils with the heavy clay subsoils comparable to the Olivenhain or Las Flores, or the hardpans of the Redding, the moisture supply is insufficient for a complete perennial cover and the native vegetation is frequently rather widely-spaced stunted bushes or brush. It is quite probable that through this effect of soil profile development in rendering the subsoils less pervious and promoting a widely-spaced vegetation, there may be definite relations between the degree of soil development and the occurrence of the natural mounds. In regions of still lower rainfall it usually is associated with the competition for moisture.”
Many years ago Dr. G. W. Barnes, first president of the San Diego Society of Natural History, wrote a paper on “The Hillocks or Mound Formations of San Diego, California” (Amer. Naturalist, Vol. 13, pp. 565-571, 3 figs., 1879). Barnes explained their formation as due to accumulation of wind-blown material around shrubs or clusters of shrubbery and rain wash of the surface between. However, some of the spaces between mounds are small enclosed basins which would not permit the escape of rain-washed material. The present authors believe that rain wash may have modified the mounds but that wind work has been the effective agent. A brief and still earlier account of prairie mounds occurring on the Pacific slope was given by Joseph LeConte (Proc. Calif. Acad. Sci., Vol. 5, pp. 219-220, Jan., 1874).
In a Rape: on the mounds of the Columbia Plateau, Waters and Flagler listed thirteen hypotheses to explain the origin of various types of prairie mounds and stated that, as a physiographic feature, they are polygenetic. See Waters, A. C., and Flagler, C. W., “Origin of the small mounds on the Columbia River Plateau,” Amer. Journ. Sci., Ser. 5, Vol. 18, no. 105, pp. 209-224, 8 figs. in text, Sepr., 1929.
The results of the work of C. C. Nikiforoff on the microrelief of the “hog wallow” areas of the Central Valley of California have recently been published by the U. S. Department of Agriculture. See “Hardpan and Microrelief in Certain Soil Complexes of California,” U. S. Dept. Agric., Tech. Bull. 745, pp. 1-46, 18 figs., April, 1941.
VotumE II] MarINE PLIOCENE OF SAN D1EGO, CALIFORNIA 19
pattern, so different from the almost perfect dendritic drainage pattern of the greater portion of the mesa. These ridges are generally composed of poorly stratified or unstratified sand of a reddish or brownish color, the color being due to weathering. The long ridge extending south from Torrey Pines Park appears to be an ancient beach ridge.” All of these ridges may be due to the accumulation of beach material just beyond the reach of the waves during a temporary halt of the regressing sea, or some of them may have been formed in the same manner as offshore bars.*° They are interesting
physiographic details of the San Diego region and are worthy of careful study.
The San Diego Mesa is but youthfully dissected by stream erosion, there being considerable interfluve area as yet uncut by running water. The northern portion, especially the mesa immediately adjacent to the south rim of Mission Valley and the Linda Vista Terrace north of it, is less dissected and hence more youthful than the southern portion, probably due partly to the harder rock in the Mission Valley region and partly to the closer spacing of the major stream valleys south of Las Choyas Valley. These valleys were cut by rivers with sources in the mountains far to the east and have histories which began before the initial stage of subaerial erosion on the relatively recently uplifted mesa. The Linda Vista Terrace is a fine example of the youthful stage of the normal cycle of stream erosion. It represents early youth, whereas the southern portions of the San Diego Mesa represent late youth. Throughout the San Diego Mesa region, with the exception of those portions modified by the beach ridges already mentioned, the streams have developed a dendritic drainage pattern due either to the uniform resistance or the horizontal attitude of the sedimentary strata of which the terrain is composed. Little tributary canyons have cut their way back into the mesa with little choice of direction, the many side-gullies pointing here and there like the smaller branches and twigs of a tree. In the eastern part of the mesa-lands some broad shallow valleys and low subdued hills occur which are strikingly different from the modern steep-sided V-shaped canyons cut by the present intermittent streams. These can be conveniently seen in the eastern part of the Otay Mesa but they occur elsewhere to the north. It is on the upper gentle slopes of these old valleys that the prairie mounds already described occur. While the authors did not have time to study these little subdued swales and valleys in detail, it seems possible that they were formed while the sea was cutting the terrace next below the Otay Terrace.® If such is the true explanation, then the short distance these early streams had to cut down to reach their base level accounts for their having widened their valleys to produce the low relief features usually associated with old age. In time the modern streams will dissect new V-shaped valleys within these old ones as headward erosion extends their courses farther and farther into the mesa.
Many of the canyons and valleys that cut the mesa have relatively steep sides with a sharp-angled shoulder at the top where valley side and mesa top meet (Plate 4, figure 2). This angular shoulder occurs where the mesa is capped by a thin but relatively hard and resistant conglomeratic sandstone discussed on another page as the Sweitzer formation. Wherever this formation occurs on the mesa it tends to produce steep-walled valleys, with angular shoulders. A peculiar feature of this hard sandstone layer, connected with its origin, is its unbroken extension from the top of the principal terrace, the San Diego Mesa, over the intervening slope to the next lower terrace. This can be seen at but few places (for example, in the Chula Vista region) but it must be considered as having an important bearing on its origin.
At several places on the mesa the surface layers of soil contain numerous concretionary pebbles averaging about the size of a pea, though some are a half-inch or more in diameter. These are brown in color and appear to be due to a concentration of a ferruginous cement. They are less well-
67 This ridge has been partially sectioned by the new Torrey Pines Highway Grade. Another less conspicuous beach ridge pies Balboa Park from the Natural History Museum north. See the physiographic block diagram for occurrence of these and other features.
68 The origin and development of offshore bars has been described by D. W. Johnson in “Shore Processes and Shoreline Development” (John Wiley and Sons), 1919, p. 365 et seq.
69 This terrace is well-developed northeast of San Ysidro (which is 1.6 miles N.W. of Tijuana) at an elevation about 50 to 75 feet below the Otay Terrace. It was included in the Otay Terrace by Ellis (1919, pl. 6).
20 San Dreco Society of Naturat History {[Memorrs
developed beneath the surface and Fairbanks” has noted that they decrease in size to a depth of about 2 feet below the surface where they cease entirely. These little nodules are quite abundant at some places, such as on the upper surface of parts of Point Loma and on the Linda Vista Ter- race, sometimes forming a layer of loose spherules on the surface of the soil. They seem to be present only where Eocene rocks occur beneath the surface, for the authors failed to note any of them on the Pliocene mesa south of San Diego River.
The principal terrace, here called the San Diego Mesa, is probably represented by parts of the upper surface of Point Loma, though faulting has tilted some of the remnants. It is also represented by a less obvious surface about half-way up the southern and western slopes of Soledad Mountain, where it has likewise been been tilted by diastrophism.
The surface of San Diego Mesa has been developed almost entirely on Eocene and Pliocene rocks, the older rocks to the east probably having been too resistant to wave erosion to have been much reduced during the time the sea was at the proper elevation to truncate the Tertiaries. In the vicinity of La Mesa it is probable some terrace cutting (marine denudation) has truncated the pre- Eocene crystalline rocks, but the exposures are not good. Marcus Hanna mentioned remnants of wave-cut cliffs at the eastern margin of Linda Vista Mesa, but these were not studied by the present authors.
Younger Terraces
The western margin of the San Diego Mesa and the sides of some of the larger valleys contain well-preserved remnants of lower, younger terraces. In the San Diego Quadrangle, Ellis’’ has described and mapped five terraces including the Otay Terrace (= San Diego Mesa) but not including the coastal flats.’* Beginning with the one next younger and just below the Otay Terrace, there are: the Avondale Terrace, with an elevation of from about 200 to 250 feet (Plate 5, figure 2); the Chula Vista Terrace,’* 100 to 130 feet in elevation; the Nestor Terrace, 25 to 100 feet in elevation; and the Tia Juana Terrace, 20 to 50 feet in elevation. Aside from these named terraces and the Sub-Otay Terrace included in the Otay Terrace by Ellis, there are still other but smaller, poorly developed and imperfectly preserved intermediate terraces.. Progressing south from Otay Valley these terraces occur at higher elevations and are separated by greater vertical intervals. As all the terraces, including the San Diego Mesa, are remnants of plains of marine denudation (and possibly to a very small extent, of marine deposition) and hence must each have been formed at approximately the same elevation during successive still-stands of the sea with respect to the land, it is apparent that uplift has been greater and more rapid as the Mexican Boundary is approached from the north. As it seems probable that most if not all of the terraces are probably not younger than middle Pleistocene, they testify to the lack of orogenic diastrophism in this region during a time when a large part of southern California north of the San Diegan district was undergoing diastrophism of considerable intensity.
These terraces warrant more intensive field work than the authors were able to devote to them. Some of them extend a considerable distance up the major river valleys. This latter fact has an inter- esting bearing on the ages of the valleys, and of course the older terraces in the mountains to the east also present evidence bearing upon the physiographic history of the region as a whole.
Older Terraces
In the foothills and mountains of crystalline rocks east of the coastal mesa region an older higher
70 Fairbanks, H. W., Calif. State Mining Bureau, llth Ann. Rept. State Mineralogist, p. 98, 1893. Marcus Hanna likewise notes these concretionary nodules and gives two figures of them. See Univ. Calif. Publ. Bull. Dept. Geol. Sci., Vol. 16, no. 7, pp. 218-219, pl. 23, figs. 1, 2, 1926.
71 Ellis, A. J., in Ellis, A. J., and Lee, C. H., U. S. Geol. Surv., Water Supply Paper 446, pp. 25-28, pl. 6, 1919.
72 Ellis did not recognize the terrace 50 to 75 feet below the Otay Terrace which is quite distinct in the region just northeast of San Ysidro. This terrace, which we here call the Sub-Otay Terrace, may have a genetic connection with the prairie mounds and earlier cycle stream valleys briefly discussed in this paper.
73 Marcus Hanna calls the prominent terrace extending from La Jolla south to Pacific Beach at an elevation of from about 25 feet in the south to nearly 200 feet in the north, the La Jolla Terrace, but he believes it probably corresponds to the Chula Vista Terrace of Ellis. (M. Hanna, 1926, p. 194).
VotumeE II] MariINE PLIOCENE OF SAN D1EGO, CALIFORNIA 21
terrace can be readily seen. This was described by Ellis, and later by M. Hanna, as the Poway Terrace, due to its conspicuous development on the hilltops south of Poway Valley (in the northeastern part of La Jolla Quadrangle). The western part of this terrace is better developed in the northeastern portion of the La Jolla Quadrangle, north of the San Diego River, than it is farther south. East of the Linda Vista Mesa it can be seen at the tops of the hills, beginning at the west with an elevation of between 800 and 900 feet but sloping upward toward the east at the rate of about 50 feet per mile, so that elevations of 1,100 to 2,100 feet are attained in the El Cajon Quadrangle 5 to 20 miles to the east. It is probable that this higher older surface should be referred to as an old-land surface which had reached the old age stage in the cycle of subaerial erosion before the general post-Pliocene elevation”* of the entire coast. This old-land surface is preserved on parts of the upper drainage basin of the San Diego River where recently cut canyons with V-shaped cross sections have only partly dissected the rolling upland.”? This surface probably had many monadnock hills and peaks and thus was not a true peneplain although some of its present vertical irregularities may have been caused by later faulting.”° In the paper on the water resources of western San Diego County referred to above, Ellis included a preliminary map of the County (1919, pl. 3) on which numerous faults and lines of topographic expression which suggest the presence of faults are delineated. Although the present authors were prevented by limitations of time from making a careful field study of the mountainous region, they believe that some faults will eventually be clearly established and that the northwestward trending fault bounding Warner’s Ranch Valley (San Jose del Valle and Valle de San Jose land grants) and the Palomar Mountain mass on the southwest is quite definite. The fault on the southwest margin of this valley has been considered by Sauer to be an extension of the Elsinore fault which borders the northeastern front of the Santa Ana Mountains farther northwest.”
In parts of the region around Potrero and extending with interruptions far to the east of Campo and also for an unknown distance south into Lower California, Mexico, there is an old-land surface which is probably equivalent to the surface developed farther north. Sauer (1929, pp. 222, 248) has considered this “rude general level of the western flank of the highland, extending far into Lower California,” a much dissected and warped Eocene marine terrace (p. 248). In arriving at this conclusion he may have been influenced by the possible genetic connection between the Poway conglomerate in the La Jolla Quadrangle, now considered to be of upper Eocene age, and the hilltop gravels which extend in an interrupted belt from near Witch Creek in a southwesterly direction towards the hills of Poway conglomerate east of Miramar. These hilltop gravels may or may not be the fluviatile phase of the Poway conglomerate; but if they are, they represent fragments of a formation which has, through the vagaries of long periods of erosion, escaped complete destruction. We do not believe they can be used to fix the date of the development of the old-land surface, since it seems more probable that subaerial erosion during Pliocene times is responsible for that feature of the topography. We know of no marine Eocene fossils occurring on this old-land surface and are disinclined to believe a marine transgression of the sea so far to the east occurred during Tertiary time.
That parts of this old-land surface were exposed to subaerial agents for a considerable period seems to be corroborated by very deep weathering. Water supply and reservoir site investigations
74 In his paper on “The Post-Pliocene Diastrophism of the Coast of Southern California” (Univ. Calif. Bull. Dept. Geol., Vol. 1, no. 4, pp. 115-160, pls. 8, 9, 1893), Lawson first clearly called attention to the importance of Quaternary uplift along this portion of the Pacific coast.
75 Merrill (Calif. State Mining Bureau, Biennial Rept., 1913-14, p. 8, 1914. Quoted by Ellis.) believed that faulting and folding was largely responsible for the irregularities of the topography of this upland area.
76 Ellis (in Ellis, A. J., and Lee, C. H., U. S. Geol. Surv., Water Supply Paper 446, p. 48, 1919) called attention to the plain-like slope of the highland area, and indicated a number of faults.
77 Carl Sauer, in an important and interesting paper on “Land Forms in the Peninsular Range of California as Developed about Warner’s Hot Springs and Mesa Grande” (Univ. Calif. Publ. Geography, Vol. 3, no. 4, pp. 199-290, pls. 21-41, 5 text figs., Dec., 1929), has described the physiography and explained the topographic development of a portion of northeastern San Diego County. A carefully prepared map is included which explains the author’s interpretation of the kind of land surfaces represented and also the major faults. Sauer emphasizes the effect of denudation, sensu stricto, in producing concave land slopes, and stream erosion in producing convex surfaces. His analysis is based upon the somewhat deductive methods of Walther Penck (in that author’s “Die Morphologische Analyse”), some of whose interpretations of land forms have been challenged by W. M. Davis (see “Piedmont Benchlands and Primarriimpfe,” Bull. Geol. Soc. Amer., Vol. 43, pp. 399-440, 10 figs., June 30, 1932).
22 San Dreco Society oF NaturaL History {Memorrs
have shown that the granitic rock in some cases is weathered at least partially and is somewhat porous to a depth of 100 feet.”*
SHORELINE FEATURES
The configuration of the shoreline of southern San Diego County is irregular due to differences in geologic structure and rock hardness. Wave erosion has etched out the resistant rock masses and the prograding or constructional work of the shoreline processes has tended to close up the embayments, resulting in rocky forelands between which are bays and sandy beaches. North of La Jolla the Tertiary Mesa composed of rocks of almost equal hardness has been evenly truncated by wave erosion, resulting in a long series of sea cliffs at the foot of which is a narrow beach. The land seems to be sinking slowly with respect to sea level, which permits the larger waves during storms to attack the base of the cliffs, oversteepening them and reducing them by landslides and other processes of cliff destruction. Observations of the lower southern portion of the cliffs at the Scripps Institution of Oceanography of the University of California, just north of La Jolla, show a rapid rate of retreat.”? Along this part of the coast the marine cycle of shoreline development has reached a mature stage. No promontories remain and the coastline is a long gentle curve. About a mile south of the Scripps Institution the coast line projects out about a mile due to the resistant nature of the hard Cretaceous sandstones which outcrop there at sea level. Here the waves have sculptured the rock in a variable manner due partly to differences in induration of the successive beds of sedimentary rock, but probably more largely due to the jointing and concretionary nature of the sandstone. Caves, small arches and irregular stacks have been etched out by wave erosion. What appears to be a recently uplifted wave-cut terrace, a few feet above high tide, may be a small bench cut by exceptionally high waves during occasional storms. Southward from La Jolla the shoreline continues irregular for about three miles until Pacific Beach is reached. There the less resistant Eocene and Pliocene sediments have yielded more readily to wave attack and this feature, probably in combination with a local structural low, has produced a mature shoreline.
The material eroded from the shore south of La Jolla and more particularly from the embankment cut into the terrace upon which the community of Pacific Beach has been built, as well as the sediment brought to the shore by the small intermittent streams draining the western slope of Soledad Mountain, has been shifted southward by the coastwise currents, assisted by the waves, and deposited almost completely across the mouth of Mission Bay (formerly known as False Bay, and by the early Spaniards as Puerto Falso), resulting in a long sand spit with a narrow tidal opening at the south. This is now known as Mission Beach. Underlying the sandy surface of this sand spit, at about mean sea level, and below, numerous cobbles occur which have been encountered in test pits dug by the City Engineer of San Diego.
Mission Bay seems to have had a structural origin. It may be the submerged southern downwarped part of the Soledad Mountain block. If this is the true explanation, hidden faults probably exist near its eastern and southern margins. A fault bordering the east shore of Mission Bay is suggested by the difference in altitude of Eocene beds on opposite sides of Rose Canyon, the presence of a small spring”’ near the bay shore between Atwood and Morena, 2.55 miles north of the San Diego River dike on U. S. Highway 101 (Pacific Boulevard),*' and a tilted block of Eocene strata which formerly
78 Professor C. F. Tolman, verbal communication, 1935.
79T. W. Vaughan (Science, New Ser., Vol. 75, no. 1939, p. 250, Feb. 26, 1932) has recorded a 20 foot recession of a cliff 21 feet high in 12 years, and lesser recessions of higher cliffs.
Lakes discussed details of erosion of the cliffs along the seaside at La Jolla. (Lakes, Arthur, “Geologizing by the Seaside. Illustrations of Geologic Phenomena related to Mining as shown in the Sea Cliffs and Caves at La Jolla, near San Diego, California,” Mines and Minerals, Vol. 23, no. 12, pp. 543-545, 6 figs., July, 1903. — “The Sea and Mining. Illustrations Shown at Sea Coast of Manner of Making and Destruction of Rocks by Action of Shellfish and Erosion,” Mines and Minerals, Vol. 24, no. 1, pp. 12-14, 6 figs., Aug., 1903).
80H. W. Fairbanks mentioned a large tufa deposit on the “southern” shore of False Bay. See 11th Ann. Rept. Calif. State Mineralogist, p. 97, 1893. A letter from the late Frank Stephens, dated Aug. 27, 1937, states that in his opinion the spring mentioned by Fairbanks is the one on the east shore of Mission Bay.
51! This spring, which is now a mere seep, is 2,376 feet north along U. S. Highway 101 from a point where joined by Jellert Street. This is a little north of where Edison Street, if projected, would intersect the highway. Tufaceous material is exposed in the road embankment for about 100 yards near the spring.
Vo.umeE II] MarINE PLIOCENE OF SAN DIEGO, CALIFORNIA 23
existed north of San Diego River north of Old Town.** A possible southern (east-west) fault is entirely hypothetical but appears to be strongly suggested by the structural relations in this region. The chief characteristics of Mission Bay at the present time are its very shallow depth of water, and the large delta of the San Diego River which threatens to encroach farther and farther upon the remainder of the Bay.** It seems possible that Salicornia sp. and Spartina leiantha Bentham and other salt and brackish marsh plants may play some part in reducing the area of occasionally submerged portions of tidal flats in this region. The Spartina, particularly, may be effective in accelerating deposition since it grows largely below mean high water** and tends by its presence to reduce the velocity of currents transporting sediment during times of flood or storm. The Salicornia, on the other hand, grows mostly above mean high water, and is only partly inundated by extreme high tide. It tends to prevent erosion, however, and gradually adds to the sedimentary layer by the accumulation of a “peaty” material composed of its dead stalks and roots.
The small intermittent streams which occasionally flow from Tecolote Valley and Rose Canyon have built small deltas which likewise reduce the volume and area of the bay. Projecting south into the bay from Pacific Beach is a broad point which is an extension of the La Jolla Terrace. This is known as Bay Point or Crown Point. Its surface is largely covered with windblown sand which is now weathered a light yellowish brown. It may have been built in somewhat the same manner as the Mission Beach sand spit. Below the covering of aeolian sand, Crown Point is composed of late Pleistocene fossiliferous cross-bedded sands and silts, and is either an ancient sand spit or the wave-built portion of the La Jolla Terrace (Plate 14). When the sea submerged Crown Point, the coastal currents must have swept over what is now the low ground between Mission Bay and San Diego Bay, isolating Point Loma as an island.
All of the low flat land between Old Town and the northeast margin of Point Loma is a delta deposit of the San Diego River.*’ This river and its distributaries occupied many different positions on the growing delta. In 1849 it was flowing into San Diego Bay, according to the manuscript map of Lieutenant Cave J. Couts of the First Dragoons, U. S. Army.*® The San Diego River is also depicted as flowing into San Diego Bay in the “Official Map of the Pueblo Lands of San Diego” compiled by Charles H. Poole, U. S. Deputy Surveyor, in 1856, and in the U. S. Coast Survey Map
82 This tilted block had an east-west strike and dips 45° south. This little hill has been completely removed by grading operations.
83 A relatively short time ago this bay must have had a considerably greater depth of water, for Sebastian Vizcaino referred to it as a good harbor, and Derby in 1853 (Senate Exec. Doc. 1, 33rd Congress, Ist Session, pt. 3, p. 111, 1853) stated: “Before 1810 the False bay was sufficiently deep to admit of the ingress of vessels of very considerable size; at present it is filled with shoals and sand bars, and has hardly sufficient water at low tide for an ordinary sail-boat.”
84 According to the investigations of Dr. Ira L. Wiggins of Stanford University, at the Mission Bay Causeway Spartina ranges from 1.43 feet to 3.92 feet above Mean Lower Low Water in Mission Bay. The lower limit of Salicornia here is 3.64 feet above Mean Lower Low Water. Mean High Tide in Mission Bay is 3.70 feet above Mean Lower Low Water. The latter datum in Mission Bay is 1.21 feet above that of La Playa in San Diego Bay. The lower limit of both Distichlis and Frankenia, when present, is always just above mean high water. According to Dr. Wiggins, these salt marsh plants have a slightly different vertical range at other localities. For example, at National City on San Diego Bay, where Mean High Water is 5.20 feet above Mean Lower Low Water at La Playa, Spartina ranges from 3.46 to 5.93 feet, Salicornia has its lower limit at 4.65 feet, Distichlis lives as low as 5.56 feet and Frankenia has a lower limit at 5.66 feet.
85 G. H. Derby, Lieutenant of Topographical Engineers (Senate Exec. Doc. 1, 33rd Congress, Ist Session, pt. 3, 1853, p. 111) in 1853 made the following statement in regard to this delta plain: “Judging from the topography, it may be supposed that the False Bay and San Diego harbor were originally one sheet of water, the sandy plain now separating them having been formed by the deposits of sand from the river; if this was the case, it was before the settlement of this part of the country, as none of the old Spanish residents remember, or have any tradition of such a thing. I have, however, been told of the existence in San Francisco of an old Spanish chart on which the bays are thus represented.” See also J. Kearney, pp. 257-262, in same document.
86 Now in possession of Mr. Cave Johnson Couts of the Guajome Rancho, near Oceanside, San Diego County. This map, dated April 28th and 29th, 1849, is one of several showing the route traversed by Lieutenant Couts’ Command during this period.
See also report of G. H. Derby (Senate Exec. Doc. 1, 33rd Congress, Ist Session, pt. 3, 1853, p. 110) in which he made the following statement regarding the former positions of the mouth of the San Diego River: “At the time of the first establishment of the Mission of San Diego, and the ‘Presidio,’ or military post, this plain, and in fact the whole valley for six miles above, was covered with a dense forest of sycamore, willow, and cotton-wood, with an undergrowth of various kinds of shrubbery, among which the wild grape was most abundant. At this time the river ran through the most northerly part of the plain, skirting the hills represented on the plan, and emptied into False bay. This course it continued until 1811, when, by the continued deposit of sand, its bed was so much elevated that it altered its channel to the southwest, still however emptying into False bay, until 1825, when a great freshet occurring it overflowed its banks, destroying many gardens and much property, and formed a new channel discharging into the harbor of San Diego. From the continued accumulation of sand its course has somewhat fluctuated but has never been essentially altered since that period.”
24 San Dreco Society oF Natura History (Memorrs
of this region dated 1859. A portion of this latter map has been reproduced in our Plate 1. It shows an older channel of the San Diego River leading into False Bay. The high rate of deposition from the river threatened to destroy San Diego Bay as a harbor and the Federal Government diverted San Diego River into False Bay (now called Mission Bay) in 1853 by the construction of a dike.
A levee or embankment of earth was built from a point near Old Town to a point on the opposite highland on the north end of Point Loma, a distance of about 3,570 feet. This was built under the direction of Lieutenant George H. Derby,’ U.S. Topographical Engineers. Work began*® on September 19, 1853, and apparently was completed®? on November 20, 1853. Later on that same year heavy rains caused the river waters to wash out a part of the levee and the river resumed its course into San Diego Bay.”° It continued in this course until 1876’ when an adequate earthen embankment was constructed which has permanently forced the river into False Bay (see Plate 15, figure 1).
Since the completion of the levee of 1876 a considerable volume of sediment has been added to the San Diego River delta in Mission Bay. In 1937 the State of California employed a civil engineer, Norman O. Glover, to resurvey the profiles surveyed in the delta region by Lieutenant John H. Weeden, U.S. Army Engineers, in 1875. Weeden’s base line was reestablished and his elevations adjusted to coincidence with the new levels at the summits of two low knolls of Quaternary non-marine reddish sandstone in the delta flat north of the west end of the present levee. A comparison of these profiles indicates no significant change in elevation of the flats south of the levee, but north of the levee much of the surface is now from 2 to 4 feet above that of 1875.” A brief field study of a portion of the delta of the San Diego River north of the levee has shown that a deposit of light gray medium-grained sand, containing abundant brown and yellow weathered biotite mica, about 2 to 4 feet thick, overlies a brown sandy or silty clay. The upper layer of gray sand may represent the material deposited by
87 For an account of Derby’s work in California see “The Topographical Reports of Lieutenant George H. Derby,” Introduction, by Francis P. Farquhar, Quarterly of the Calif. Hist. Soc., Vol. 11, no. 2, pp. 99-102, June, 1932. Reprints of Derby’s reports occur in no. 2, pp. 102-123, 2 maps, June, 1932; no. 3, pp. 247-265, 1 map, Sept., 1932; no. 4, pp. 365-382, 1 map, 6 sketches, Dec., 1932. The separates containing these reports issued by the Calif. Hist. Soc., Spec. Publ. 6, 1933, contain additional information not included in the complete volume. See especially pp. 65-71 for information regarding Derby’s work at San Diego.
88 See The San Diego Herald, Vol. 3, no. 33, p. 3, col. 5, Sept. 24, 1853. “This work was commenced by Lieut. Derby, U. S. Corps of Topographical Engineers on Monday last [Sept. 19, 1853]. His orders are to excavate the former channel of the river discharging into False Bay and to build a levee or embankment of earth from a point near the Old Town to a point on the opposite high land (distance 1,190 yards) intersected by the Playa road to counteract the action of subsequent freshets. Sixty laborers with carts, wheelbarrows, etc., are to be put on the work at once”...
89 Letter from Lieut. George H. Derby to Col. J. J. Abert, Chief Topgl. Engineers, San Diego, Nov. 20, 1853. “I have the honor to inform you that the work on the San Diego River was this day completed, in the manner described in my report of the 15th Oct. ult.” (Letter on file in the archives of the U. S. Army Engineers, War Department, Washington, D. C.).
90 See the San Diego Herald, Vol. 5, no. 1, p. 2, col. 4, April 21, 1855. “We mentioned some time ago that a part of the dam which Lt. Derby, U. S. Top. Eng., erected, for the improvement of San Diego harbor had given away under the pressure of water caused by the first heavy rains, and that the river, which had been turned into False Bay, was running in its original channel. In four years we have never known the water to be so high as this season. The rain which fell during the early part of the week has had the effect to considerably widen the breach in the dam and if something is not done before the next rainy season to repair the damage the amount of the outlay which has already been made, will be worse than thrown away.”
91 On June 5, 1876, ground was broken for the new levee which was completed on Nov. 6 of the same year. Ann. Rept. Chief of Engineers [U. S. Army] for 1876, pt. 1 (44th Congress, 2nd Session, House of Representatives Ex. Doc. 1, Vol. 2. pt. 2, 1876), p. 114; Ann. Rept. Chief of Engineers for 1877, pt. 2 (45th Congress, 2nd Session, House of Representatives Ex. Doc. 1, Vol. 2, pt. 2, 1877), Ap. II, p. 998.
Additional information regarding the dike can be found in the Ann. Rept. Chief of Engineers for 1874, pt. 1, p. 119, pt. 2, Ap. AA3, pp. 372-375; 1875, pt. 2, Ap. FF2, pp. 723-724; 1878, pt. 1, p. 136, pt. 2, Ap. II1, pp. 1301-1302. According to accounts the north side of the levee was faced with a heavy stone wall which rested on a stone foundation five feet deep. The levee was over 7,000 feet long, 15 feet wide at the top, 40 feet wide at the base, and 5 feet high. See also the San Diego Union, Sept. 11, 1876.
The earth used in the construction of the dike came in part from the cliff at the northeastern end of Point Loma near the Present intersection of Mission Bay Causeway and West Point Loma Boulevard and in part from the site of the fort on the point of the hill below the old Presidio at Old Town. According to a local historian: “Nothing whatever of the site [of the old fort] now remains, the earth forming the point of the hill having been hauled away and used by the government engineers in making the embankment for turning the San Diego river, in 1877. Some of this earth was also used for grading the county road across the valley from the end of the Old Town bridge, in later years. These excavations also took large quantities of earth from the north side of the hill, the extent being measured by the widening of the road from a narrow track to its present width.” (See Black, Samuel F., “San Diego County, California. A Record of Settlement, Organization, Progress and Achievement,” The S. J. Clarke Publishing Co., Chicago, p. 82, 1913).
92 See testimony, and plaintiff's exhibits Nos. 3 and 9, People of the State of California vs. Charles E. Arnold et al. No. 84864 Superior Court San Diego County, Hon. Chas. C. Haines, Judge, 1938.
VotumeE II] MarINE PLIOCENE OF SAN DrgEGO, CALIFORNIA 25
the San Diego River during the flood discharges since 1875. At one locality this sand contained a specimen of Physa, a fresh water shell, and at another, a piece of broken Indian pottery.
Like most streams in this region the San Diego River is characterized by infrequent floods” during which a large amount of sediment is carried to its delta. These occasional floods have been the effective agent in building the delta because the river is generally dry during late summer and autumn and may be dry for an entire year or more. The construction of the El Capitan Dam** on the San Diego River about seven miles above Lakeside in 1935 may reduce the frequency and violence of future floods and delay the growth of the delta in Mission Bay from now on.
In addition to the growth of the delta of the San Diego River in Mission Bay, some shoals and small islands have been formed in that shallow body of water by the action of tidal currents and waves. The light areas shown on Plate 17 at the western extremity of the deltaic region (extreme right middle part of view) are small dune ridges, two of which reach an elevation of about 10 feet above Mean Lower Low Water. The sweep of the currents in and out of the narrow entrance channel of Mission Bay tends to deposit a submarine bar off the ocean end of the entrance and tidal inlet delta shoals within. Wherever the incoming currents spread over a greater cross-sectional area their velocity diminishes and consequently their power to transport sediment decreases. The first rapid decrease in velocity occurs just within the entrance to the bay and there a prominent shoal occurs which is exposed at low tide. It is an incipient tidal inlet delta island which has nearly reached the plane of Mean High Water. As the incoming currents flow northward east of the Mission Beach spit they fan out over a larger area and deposit some of their load of sediment across the bay floor west of the causeway and southwest of the south end of Crown Point. The shoaling here has been sufficient to permit a luxuriant growth of Spartina. Some of the Spartina-covered shoal areas are shown to the right of Crown Point on Plate 17. Other Spartina-covered shoals east of the causeway seem to indicate further spreading out of the currents. The reduction of the tidal prism in Mission Bay has undoubtedly slowed up this island-forming process. At a previous time, when the river delta was smaller and the volume of tidal water was larger, the currents were more effective and tidal current island formation took place on a larger scale. It seems highly probable that a portion of the deltaic area west of the causeway was originally formed as a tidal inlet delta island. Field studies by Grant and the mechanical analysis of sediment samples tend to confirm this theory. The formation of such islands has been recently described by Lucke.”
Point Loma is a long promontory extending from the tidal flats of Mission Bay for a distance of over six miles to the south. It land-locks the western portion of San Diego Bay. Its northern part is nearly three miles wide but it narrows toward the south to a little over one-half mile near the extreme point. Its truncated top averages just over 300 feet in elevation except in the northern broader part which is somewhat lower. The terraced top may have originated at the same time as the San Diego Mesa, and its isolation may be due to relatively recent (possibly late Pleistocene) foundering of the formerly continuous land on one or more sides.*® Parts of its eastern and western shoreline are bordered by a narrow terrace with an elevation up to 25 or more feet. Stephens considered this terrace as well as the La Jolla Terrace (the Nestor Terrace of Ellis) the result of a submergence following the great Pleis- tocene emergence. Point Loma does not exhibit the well-defined intermediate terraces which characterize the western margin of parts of the San Diego Mesa. The western shoreline of Point Loma is irregular
93 According to Mr. H. B. Lynch, consulting hydraulic engineer of Los Angeles, floods occurred in the San Diego River in the following years: 1811; 1825 (San Diego River broke into San Diego Bay); 1839-40; 1855; 1857; 1862; 1873-74; February, 1884; December, 1889; January, 1916; February, 1927.
Mr. Fred D. Pyle, Hydraulic engineer for the City of San Diego, states in a letter dated November 24, 1939:
“Two years ago in studying the preliminary flood control problems of the San Diego River, the Army Engineers reported floods of maximum intensity in the following order: 1862, 1916, 1825, 1927. The 1883-84 season produced by far the most water of any year of historical times but did not produce maximum intensity of floods comparable to those mentioned above.”
Early floods in the San Diego River are mentioned by several historians. See Gunn, Douglas, “Picturesque San Diego, with Historical and Descriptive Notes” (Knight and Leonard Co., Chicago), 1887, p. 25.
94 This dam, which began to impound water Jan. 8, 1935, has a capacity of 38,000,000 gallons.
95 Lucke, J. B., “A Study of Barnegat Inlet, New Jersey, and Related Shoreline Phenomena,” Shore and Beach, Vol. 2, no. 2, pp. 5-54, 1934. — “A Theory of Evolution of Lagoon Deposits on Shorelines of Emergence,” Journ. Geol., Vol. 42, no. 6, pp- 561-584, 11 text figs., Aug.-Sept., 1934.
_ 96 Fairbanks mentions a “strong sulphur spring exposed at low tide” at the end of Point Loma. We did not locate this spring during our field work. It may have some bearing on faulting. See 11th Ann. Rept. Calif. State Mineralogist, p. 97, 1893.
26 San Dieco Soctety oF Natura. History [Memorrs
in detail due to the hard Cretaceous rocks exposed at sea level.
San Diego Bay is an elongate, irregular crescentic, land-locked body of water connected with the ocean by a narrow tidal channel on the east side of Point Loma. The entire southern and southwestern shore of the bay consists of North Island and Coronado Island and the sand spit which connects them with each other and both of them to the mainland at the south. North Island and Coronado Island may be remnants of the Nestor Terrace, as supposed by Ellis,”” but their connection to the mainland is due to a long crescentic sand spit which appears to have been constructed by the northward shifting of material brought to the shore by the Tia Juana River which reaches the sea near the Mexican Boundary. Spanish Bight is a small, shallow re-entrant of San Diego Bay between North Island and Coronado.”
Except where occasional dredging has maintained a deep-water navigable channel, San Diego Bay is relatively shallow. Tidal scour at the entrance has been assisted by a jetty. This jetty, known as the Zuninga or San Diego Jetty, may have had some important effect upon the currents and wave action along the ocean shore of Coronado and North Island. Shortly after it was built, large waves during a storm in the spring of 1905 eroded away a large part of Ocean Boulevard west of Hotel del Coronado. In regard to the construction of this jetty, Lieut. Col. R. A. Wheeler, Corps of Engineers, U.S. Army, states in a letter to us dated Washington, D. C., July 29, 1938: “The river and harbor act approved September 19, 1890, authorized the construction of a jetty 7,500 feet long on Zuninga Shoal with a view to securing a depth of 26 feet on the outer bar. The jetty, of rubble stone construction, was built to the height of extreme high water and was completed in 1904. The annual report of the Chief of Engineers for 1937 states that the jetty has deteriorated to the extent of about 75,000 tons of stone displaced.” According to a report by Colonel Chas. T. Leeds to Mr. M. W. Reed, City Manager of the City of Coronado, the Zuninga Jetty was begun in October, 1893, and its construction continued intermittently until its completion in July, 1904. In a report by Mr. D. E. Hughes, Assis- tant Engineer, to Lieut. C. T. Leeds, dated April 26, 1910, it is stated that following the extension of the Zuninga Jetty in 1900, erosion occurred just west of Spanish Bight, so that the railroad tracks supplying material to build Battery Meed (just northwest of the root of the jetty) had to be moved in 1901. Erosion began again during the next extension of the jetty in 1903 to 1904, this time farther east along Spanish Bight and eastward. ;
A small stone jetty or breakwater was built just southeast of the Hotel del Coronado in 1897 and 1898 to protect the hotel from wave erosion. It was repaired and extended at a later date.” Although the prevailing direction of drifting of beach material along the Silver Strand southeast of the hotel property appears to be toward the northwest,'°° the beach adjacent to the hotel property came under the influence of the Zuninga Jetty when it was extended to its full length. According to a report dated January 8, 1909, by Mr. Andrew Ervast, then Engineer of the Coronado Beach Com-
97 Ellis, A. J., in Ellis, A. J., and Lee, C. H., U. S. Geol. Surv., Water Supply Paper 446, pl. 6, 1919. 98 Neither of these is now a true island because they form a part of the Coronado peninsula.
99 Data from report by Col. Chas. T. Leeds to Mr. M. W. Reed, City Manager of Coronado. In addition to this break- water, “About 1900 there was constructed, a short distance east of the ‘hotel breakwater,’ and close to the bath house, a small rock groin.” By 1931 the rocks of this structure were almost completely buried in beach sand. (From rept. of Col. C. T. Leeds). In Sept., 1940, some of these rocks barely protruded above the sand.
100 Foreshore beach samples collected on Aug. 23 and 24, 1940, from the Zuninga Jetty to the Mexican Boundary showed, in general, a gradual increase in median grain size of sand particles from North Island to the mouth of the Tia Juana River. The partly decomposed golden-brown biotite flakes so abundant on the foreshore of North Island and Coronado Beach are much less common further southeast. The foreshore slope of the beach is also much steeper in the south than on North Island or Coronado Beach. The slope of the foreshore appears to be at least in part a function of grain size, and the latter is controlled by the violence of wave action. Back of the beach on North Island and back of the beach along the Silver Strand and southward to the Mexican Boundary there are small sand dunes which testify to the action of on-shore winds in removing sand from the beach. No notable accumulation of pebbles or cobbles was seen in this sand dune area except south of the mouth of the Tia Juana River, where a large number of flattish pebbles 1 to 4 inches long lie mostly buried in the sand of the eastern part of the small dunes, (see Plate 5, figure 1). Dr. Cordell Durrell, who examined these pebbles for us, determined them as dominantly hard metamorphosed andesitic and rhyolitic porphyries with occasional specimens of lime silicate hornfels. They are probably of pre-Cretaceous origin. They probably represent a local accumulation of material eroded from the bluffs of the Pliocene rocks back of the beach just south of the International Boundary. That they do not represent a concentration of gravel from the Tia Juana Valley alluvium is apparent from the fact that specimens of hornblende-rich andesite, basalt, and other non-metamorphics are absent in the beach deposits, but are common in gravel lenses in the valley fill encountered in well cores a mile or two east of the beach. The pebbles in the valley fill are, in general, less well rounded than those near the beach.
VotumE IT] Marine PLIOCENE OF SAN DIEGO, CALIFORNIA 27
pany and City Engineer of Coronado, local news items in the San Diego Union,’ and data assembled by Col. Chas. T. Leeds, storms in January, 1905, (during flood tide on about the 4th and 20th of the month), on February 5th, 1905, and again during the middle of March, 1905, caused serious wave erosion along the Hotel del Coronado grounds and Ocean Boulevard just west thereof. Mr. Ervast’s report mentions that along Ocean Boulevard a total width of 110 feet of land was removed by the waves, leaving a vertical bank 6 to 18 feet high. To prevent further erosion such as was caused by these storms, a seawall of quarry-run stone 5,200 feet long was built from the hotel westward along Ocean Boulevard between August, 1906, and October, 1907. It was repaired in 1912 and 1928.
The mainland shore of San Diego Bay is mostly salt marshes and tidal flats, except where the presence of the Nestor Terrace produces a small bluff just above high tide line. The small inter- mittent streams from Las Choyas, Sweetwater and Otay Valleys have constructed small marshy deltas.
Tia Juana’ River, which flows into the ocean south of San Diego Bay, has not produced a delta because the waves and currents have been effective in removing the sediment as fast as it is brought within their reach.' However, the river-transported silt has caused a gentle projection of the coast, but present day sinking of the land has resulted in salt marshes and small tidal lagoons behind the spit-like sandy beaches which are witnesses of the greater strength of the waves and long-shore currents. The northward shift of the sediments is due to either an eddy on the lee or southeast side of Point Loma or to the occasional southwest storm winds whose effect, though of short duration, is greater than the prevailing but gentle west and northwest breezes.
The Nestor Terrace is continuous from the foot of the San Diego Mesa (called Otay Mesa on the topographic map) westward to the beach north of the mouth of the Tia Juana River, except for a little swale extending from the Tia Juana Valley northwesterly to the southern end of San Diego Bay. This small drainage depression crosses the road just west of Nestor and Palm City. It appears to represent a channel eroded by occasional overflow waters from former great floods in the Tia Juana Valley, but it does not indicate a former course of the Tia Juana River into San Diego Bay. The Otay River and the Sweetwater River, which enter the bay, may have had some part in eroding a valley which is now submerged and represented by the southern part of San Diego Bay.
THE PENINSULAR MOUNTAINS
The mountains of San Diego County appear, in general, to be a series of irregularly disposed peaks and ridges transected by numerous stream valleys. If one could imagine all the valleys filled up to their margins, then one would see an old-land surface bearing numerous projecting hills and peaks but all with a gradual ascent from the foothills on the west to the highest summits on the east. This hypothetical picture, however, would not be an ideal example of the old age stage in the normal cycle of stream erosion, for faulting has entered the scene and broken up the terrain so that some blocks have been elevated more than others. Thus the general elevation is not uniform throughout a gradually eastward ascending surface. The Palomar Mountain mass, Volcan Mountain, the Laguna Mountains, and others, appear to have derived their topographic prominence at least partly by faults. These faults are in most cases hard to locate in this region of crystalline rocks except by their topo- graphic expression or zones of brecciation. It appears that the supposed presence of some faults which
101 See, for example, San Diego Union, Feb. 4, 1905, pp. 1, 3; Feb. 5, 1905, p. 5; Feb. 7, 1905, p. 6.
102 Tt should be mentioned that the spelling “Tia Juana” is that of American usage as shown on the topographic map of the San Diego Quadrangle, whereas the official Mexican spelling is “Tijuana.”
103 The discharge of sediment by the Tia Juana River will no doubt be decreased in the future, due to the construction of the Rodriquez Dam on this river about 11 miles (17 kilometers) east of the municipality of Tijuana. This dam, which has a capacity of 137,000,000 cubic meters and was completed in February, 1937, was constructed for the storage and diversion of water for irrigating about 5,000 acres in Tijuana Valley in Mexico and for domestic use of the 10,000 inhabitants of Tijuana. See Williams, C. P., “Foundation Treatment at Rodriquez Dam,” Proc. Amer. Soc. Civil Eng., Vol. 58, no. 8, pp. 1375-1385, Oct., 1932 — Trans. Amer. Soc. Civil Eng., Vol. 99, paper no. 1863, (Proc. Vol. 60, no. 8, pt. 2) pp. 295-313, 9 figs., 1934. The total drainage area of the Tia Juana River is about 1,668 square miles, of which 939 square miles are above Rodriquez Dam. Since there are about 250 square miles of drainage above Barrett Dam on Cottonwood Creek, a tributary in the United States, the lower Tia Juana River now has a total of only 479 square miles of uncontrolled drainage area below the dams. See 71st Congress, 2nd Session, House Doc. 359, “Report of American Section of International Water Commission, United States and Mexico,” April 21, 1930, Ap. 1, p. 79, and map facing p. 84.
28 San Disco Socrety oF Naturat History [Memorrs
have been reported in this region is based upon slight evidence. The trend of most of the important faults is roughly northwest and southeast, thus partaking of the general directional pattern of well- known faults farther north, such as the Elsinore fault, the San Jacinto fault, and others.
It can hardly be said yet with absolute certainty from our limited knowledge of this country that the gently rolling surface on the higher parts of the Palomar Mountains, the upland meadows and subdued hills on the summit area of the Laguna Mountains, and other similar features, are upfaulted correlatives of the less elevated but more extensive general old-land surface of the region as a whole. The existence of these subdued topographic forms so far from the coast, so high in elevation and not yet maturely dissected by the narrow, deep canyoned streams which are actively eroding their courses, suggests a recent rejuvenation of the entire region with the initiation of a new erosion cycle which has now reached only the stage of late youth.
This mountainous area is terminated on the east by a steep descent to the low depressed area of the Colorado Desert. It seems highly probable that this eastern margin of the Peninsular Range is defined by faults, but the irregular margin of the mountains, with numerous projecting ridges extending far eastward into the desert, suggests a complex series of faults rather than one fault or one fault zone, which would tend to produce a scarp of a more nearly linear character.
STREAM VALLEYS AND DRAINAGE Coastal Mesa Region
The larger valleys which have been cut through the San Diego Mesa, such as Mission Valley, Sweetwater Valley, Otay Valley and Tia Juana Valley, are characterized by flat sandy or silty bottoms and abrupt side slopes, the river channels being three hundred feet or more below the upper surface of the mesa. All these major valleys have been eroded into the relatively soft Tertiary sediments of the mesa by rivers whose headwaters are far to the east in the mountainous region where the annual rainfall is much greater than that of the coastal area. Otay Valley, unlike the others mentioned, has a broadly rounded bottom which may be due to its being a younger valley, as explained by Ellis. All these valleys owe their flat floors to aggradation, the valley fill being possibly as much as two hundred feet deep in some cases.'°* The depth of the river alluvium in the Tia Juana Valley has been determined by a geophysical survey made in connection with underground water problems. About 3,200 feet north of Monument School (which is just east of the mouth of Smallcomb’s or Smugglers’ Canyon) the bottom of the valley fill is at approximately 110 feet below mean sea level. As the surface there is just over 20 feet above mean sea level, the vatley fill is over 130 feet thick. Along a north-south geophysical traverse about 6,200 feet west of the Monument School the maximum depth of the bottom of the valley fill is at approximately 120 feet below mean sea level. This is about 500 feet north of the location of the Holderness Well mentioned in another part of this paper. It is of interest to note here that the ground water table in the Tia Juana Valley (except within the temporary depression cones sur- rounding actively pumping wells) is sufficiently above sea level to prohibit the influx of sea water beneath the fresh water under the principle of Ghyben and Herzberg.'””
During the time of greatest emergence in the Pleistocene the major streams cut deeply into the Tertiary strata but have since aggraded their lower courses. The minor valleys and the tributaries of the larger ones just mentioned are characterized by steep-sided V-shaped cross-sections. Except where the ancient beach ridges north of Mission Valley have controlled the initial post-emergent run-off
104 Ellis, A. J., in Ellis, A. J., and Lee, C. H., U. S. Geol. Surv., Water Supply Paper 446, p. 33, 1919.
105 Badon Ghyben, W., “Nota in verband met de Voorgenomen Put boring Nabij Amsterdam,” Tijdschr. Kon. Inst. Ing., 1888-89, p. 21, The Hague, 1889; Herzberg, Baurat, “Die Wasserversorgung einiger Nordseebader,” Jour. Gasbeleuchtung und Wasserversorgung, Jahrg. 44, Munich, 1901. Well explained by John S. Brown, “A study of coastal ground water,” U. S. Geol. Surv., Water Supply Paper 537, pp. 16-18, 1925. See also, Tolman, C. F., “Ground Water,” (McGraw-Hill Book Co., New York, 1937), pp. 246-247; Stearns, H. T., and Vaksvik, K. N., “Geology and Ground-Water Resources of the Island of Oahu, Hawaii,” Territory of Hawaii, Dept. Public Lands, Division of Hydrography, Bull. 1, pp. 237-238, May, 1935.
The Ghyben-Herzberg principle is strictly true only in cases of hydrostatic equilibrium, that is, when the fresh water is at a constant potential. For low potential gradients the formula expressed in the Ghyben-Herzberg theory is approximately correct, but where ground water near a pumping well or near the sea has considerable motion the dynamic equations developed by Professor M. King Hubbert should be used. In the latter case the fresh water-sea water contact under the land surface is lower than the value given by the static equilibrium formula. See Hubbert, M. King, “The Theory of Ground-Water Motion,” Journ. Geol., Vol. 48, no. 8, part 1, Nov.-Dec., 1940, especially pp. 870-873, 924-926.
VoLuME II] MarINE PLIOCENE OF SAN DIEGO, CALIFORNIA 29
and thus deflected the streams, the drainage pattern is distinctly dendritic. The steep valley sides, often with little talus accumulation at the base, are more or less characteristic of regions of small annual rain- fall, with occasional sporadic floods.
Peninsular Mountains
East of the San Diego Mesa the streams have cut steep-walled valleys into the crystalline rocks of the mountainous region which characterizes the central and eastern parts of San Diego County. The San Diego River and Sweetwater River flow for many miles through deep, steep-sided valleys, with the river beds often 500 or more feet below the old-land surface described on a preceding page. This is well shown in the view of a canyon, cut by a tributary of the San Diego River, illustrated in Plate 4, figure 1. These valleys give the appearance of being entrenched through a recent revival of erosion. San Diego River, the largest river in southern San Diego County, has a flat floor or flood plain for some miles above Lakeside, but the steep valley sides with the more or less angular shoulder at the rim of the old-land surface, and the V-shaped tributary valleys, are characteristics of youth in the present cycle of erosion. Occasional broad valleys exist in parts of the drainage basins of these rivers, such as Potrero Valley, Morena Valley, Pine Valley, Descanso Valley, and others. They are probably due to variation in rock resistance or to structural causes not determined by us. Some of the upper tributaries of San Diego and Sweetwater Rivers have their sources in swampy or damp near- summit meadows.
The drainage of the mountains is nearly all westward, the divide between streams flowing to the Pacific and those flowing to the desert being very close to the eastern margin of the mountains. The drainage pattern is very irregular, which appears to be due to structural causes, in some instances possibly due to faulting; but this problem requires much study. Ellis has indicated the probable ex- istence of a number of faults which have influenced the drainage, and Sauer has described some valleys in the Mesa Grande region which are probably genetically connected with faults.
PHYSIOGRAPHIC HISTORY
An adequate treatment of the geomorphogeny of that portion of San Diego which is briefly described, for the most part in an empirical manner, in the present paper, would require a long and intensive field study which the present authors have not been able to pursue. It is hoped that the brief outline of a probable series of more important events given here will be taken as a stimulus to an intensive study by others and not as a final interpretation or explanation of this very interesting and physiographically complex region. Gale'°® has presented some ideas on the origin of the San Diego Mesa, based largely on field data furnished by Grant.
The San Diego Mesa, composed of gently inclined Eocene and Pliocene sediments, is a plain of marine denudation, the Tertiary strata being distinctly truncated. During the deposition of the Pliocene sediments the sea must have had a position far above the present mesa surface, possibly an elevation of 800 feet or more above present sea level, or 300 or 400 feet above the present mesa level. Thus the San Diego formation of Pliocene age must have once extended far north of Mission Valley and possibly considerably east of its present limits. It is possible that a long still-stand of the sea during approxi- mately middle Pliocene time represents the period when the Poway Terrace was developed by subaerial erosion; and possibly the old-land surfaces farther east can be correlated with it. If this explanation is correct, then the fine grain size of the silts and sands of the San Diego formation (containing rela- tively little gravel and cobbles) is explained by the subdued topography from which the somewhat sluggish Pliocene rivers derived their clastic loads. This mid-Pliocene time of low relief on the land (and high stand of the sea) appears to be represented in mountains east of the mesa lands by the subdued relief and old-land features described above.
Sometime after this approximately middle Pliocene period of submergence during which the San Diego formation was laid down, there began a slow uplift and tilting westward of the entire region
( hig Gale, H. R., in Grant, 1v, U. S., and Gale, H. R., Mem. San Diego Soc. Nat. Hist., Vol. 1, pp. 45-49, diagram C p- LOSI.
30 San Dieco Society of Naturat History [Memoirs
back as far as the escarpment on the east side of the present Peninsular Range in southern San Diego County. The early phases of the faulting which have left an impress on the present physiography of the mountainous region may have begun at this period. Possibly these newly inaugurated faults resulted in the formation of enclosed or partly enclosed basins within which some of the continental sediments were deposited by the revived streams.’ The effect on the San Diego Mesa of this gradual uplift and tilt toward the west was to truncate and lower the surface of the recently deposited Pliocene sedi- ments by wave scour at the profile of equilibrium. Also, the revived streams on the land to the east began bringing to the sea coarse material which was shifted alongshore and over the sea floor by the waves. The increased erosive power of the streams, alone, might account for the bringing to the sea of the gravel and cobbles which were later to be left on the truncated mesa as the Sweitzer forma- tion, or faulting might have added heavy material to stream loads where fault scarps or shattered zones were athwart stream channels. The effect of this gradual uplift and westward tilt on the area east of the coast was to rejuvenate the region and inaugurate a new cycle of erosion. This new cycle was impressed upon the previous cycle which had not yet reached the peneplain stage but had probably attained early old age. During this period the Sweitzer formation, which lies nonconformably on the truncated mesa deposits, was formed as a stream supplied, but probably wave and current shifted, residual veneer on the shallowing sea floor.
This uplift and tilting continued, but probably at varying rates and with occasional periods of quiescence. During a time of rapid elevation the sea was unable to maintain its position over the submarine terrace of Pliocene sediments,'°* but was forced to retreat to the outer edge of the deposit where it began to cut a new terrace in them at a lower level. During the retreat of the sea off the mesa, it left behind beach ridges which still remain on the Linda Vista Mesa north of Mission Valley. At about this time or a little later it is probable that many of the prairie mounds were formed on the mesa by wind transportation of super-abundant loose clastic material not protected by an adequate cover of vegetation. Successive lower positions of the sea during the intermittent uplift resulted in the series of minor terraces which are still partly preserved on the outer marginal slope of the San Diego Mesa. The development of each lower terrace tended to areally reduce the next one above and it thus follows that the San Diego Mesa as a whole, and each lower terrace, may now be but a remnant of its former extent. Thus the continued but intermittent elevation of the land, possibly accompanied by a continuation of the westward tilt of the entire eastern orogenic block, resulted in the emergence of the San Diego Mesa and the cutting of a series of lower terraces on its seaward margin. The rivers on the land area to the east continued to be revived and were thus able to entrench themselves in steep- walled canyons below the general level of the old-land surface inherited from the previous (incomplete) erosion cycle. As soon as the San Diego Mesa emerged above the sea the larger streams, already well established in their valleys to the east, cut steep valleys through the relatively soft Tertiary sediments in their courses to the new more western shoreline of the sea.
The presence of what have been interpreted as submarine valleys off the coast of southern Cali- fornia, the great thickness of alluvium filling the bottoms of the major valleys in the San Diego Mesa, and the very incomplete known marine Pleistocene fossil record in San Diego County, all suggest an emergence of the coastal region to an elevation considerably above its present position during post- San Diego time. It was during this great emergence of the land that the larger rivers cut their beds so far below the present valley bottoms in the mesa region. Due to the much more resistant nature of the crystalline rocks east of the Tertiary sediments, none of the rivers were able to cut their channels below their present levels except in limited parts of their courses where local warping or the crushed nature of the rock near faults favored rapid erosion. Thus San Diego River and Sweetwater River at present flow over alluvial-filled valley floors in only limited parts of their courses in the foothills of crystalline rocks. It is possible that this great emergence occurred at the same time as the mid-Pleistocene
107 Reed, R. D., “Geology of California,” p. 22, footnote 2, 1933, Reed states: “Vertebrate fossils of probable upper Pliocene age have recently been found in extensive sedimentary deposits a few miles west of Warner’s Hot Springs.”
108 The truncation of the mesa was sufficient to remove all of the Pliocene sediments north of the San Diego River, and also an unknown thickness of the Eocene below. Of course, it is possible that the mesa was truncated by wave erosion entirely on a landward retreating sea cliff which began as a notch on the outer edge of the emerged terrace.
VotumeE II] MarINE PLIOCENE OF SAN DIEGO, CALIFORNIA 31
orogenic disturbance (termed the Pasadenan Orogeny by Hans Stille) that folded and faulted so much of the Tertiary and lower Pleistocene strata in the Los Angeles-Ventura region, but there are no direct means of testing this possibility at the present time. The faults in the Peninsular Range of San Diego County may have been active at this time.
As stated by Stephens and others, the period of uplift appears to have been followed by a later submergence of the coastal region by the transgressing sea which reached a position approximately 100 feet above present sea level. It was probably during this late Pleistocene transgression that upper Pleis- tocene fossiliferous sands were deposited along parts of the shore of San Diego County. Too few facts have been obtained as yet to attempt a correlation of the steps in the Pleistocene history of this region with that of other regions, such as the Palos Verdes Hills near San Pedro or the terraces along the Malibu coast so interestingly discussed by Davis.
The latest physiographic events appear to be the slow reduction of sea cliffs and beach embank- ments, the construction of spits and bars and the growth of small deltas in bays and lagoons. As a whole, the coast now appears to be sinking slowly. This might be local or it might represent an eustatic rise of sea level.
This sequence of events in the post-Pliocene history of the San Diegan region must be considered largely hypothetical and unproved. Until much detailed field work can be accomplished little more can be said that is not largely speculative or at least based upon inadequate facts.
GENERAL RELATIONSHIPS TO OTHER REGIONS
The San Diegan region, whose physiography has just been briefly discussed, is a small part of what Fenneman!” has referred to as the Lower California Province, and what Reed'’® has included in the Peninsular Ranges Province. The westward tilted and rejuvenated mountainous part of San Diego County has some similarity to the tilted fault block of the southern Sierra Nevada in east central California, but the eastern margin of the mountains in San Diego County is a more complex and ir- regular escarpment than that defining the eastern precipitous slopes of the southern Sierra Nevada and the rocks represented and their structures are only similar in part. However, in both regions old sedimentary rocks have been intruded by acidic plutonic rocks which may be of approximately the same age. The similarity of the Peninsular Range in San Diego County to the Santa Ana Mountains in Orange County is probably closer, although here again there are many important dissimilarities. Fairbanks, Hudson and others have mentioned the similarity and probable equivalence of some of the schists of the Cuyamaca Mountains of San Diego County with certain schists in the Santa Ana Mountains. The latter range is believed to be a fault block tilted westward by a fault zone along its eastern base. The San Pedro Martir Mountains, which form the mountainous backbone of the northern part of Lower California, Mexico, have been but little studied geologically but they appear to be an extension of the same general physiographic complex.'"'
The San Diego Mesa extends for some distance into Lower California, Mexico. Farther south extensive flows of vesicular lava have produced mesas which continue with interruptions as far as Ensenada, but only their general relationship to the San Diego Mesa was investigated by the authors. Other coastal terraces further south may be similar or actual physiographic equivalents.
The Tertiary strata of San Diego County are much thinner and less folded and faulted than those of the Los Angeles and Ventura Basins. The less disturbed structure of the Tertiary strata in the San Diego region may be due to their thinness and to the resistant nature of the crystalline rocks upon which they were deposited. The total absence of marine Oligocene and Miocene sediments is a striking feature. Correlations of the Pleistocene terraces of San Diego County with other California coastal regions may be possible in the future, but the basis of such correlations can only be obtained
109 Fenneman, Nevin M., “Physiography of Western United States,” (New York, 1931), pp. 508-510, and map of Physiographic Provinces.
110 Reed, Ralph D., “Geology of California,” (Tulsa, Oklahoma, 1933), pp. 20-22, map fig. 1.
111 See Woodford, A. O., and Harris, T. F., “Geological Reconnaissance Across Sierra San Pedro Martir, Baja California,” Bull. Geol. Soc. Amer., Vol. 49, no. 9, pp. 1297-1336, 5 figs., 7 pls., Sept. 1, 1938.
32 San Disco Society of Naturat History [Memorrs
by much more field work than has been accomplished up to this time. Various fault blocks may have had a somewhat independent and individual history, so that long distance correlations may be, in most cases, very difficult if not entirely impossible.'’”
PRE-TERTIARY IGNEOUS AND METAMORPHIC ROCKS
The Tertiary sedimentary formations of the San Diego region are bordered on the east by a series of volcanic breccias and agglomerates which are believed to be of Triassic age. While there is no local paleontologic evidence upon which an age determination can be based, the northern extension of this foothill belt of ancient rocks was thought by M. A. Hanna'!’ to be very similar in general characters to the dark gray or black slates and associated dikes and effusives which form the axis of the Santa Ana Mountains some miles to the north. These latter rocks were studied by Mendenhall’ who collected from them specimens of Rhynchonella, Spiriferina, Terebratula, and fragments of crinoid stems determined by Stanton as of Triassic age.
The breccias and agglomerates of the San Diego region have not been observed in contact with the Cretaceous beds by the present authors, nor by Hanna in the area immediately adjacent to the north. As stated by Hanna, however, the Eocene can be observed to rest upon the eroded surface of the ag- glomerates, and because of this relation it is reasonable to assume that the Cretaceous likewise rests upon an erosion surface of these pyroclastics. Further evidence of the considerable age of these agglomerates is their relationship to a quartz diorite batholith which has been intruded into them. In the Grossmont-Mount Helix region just east of La Mesa the diorite mass contains numerous xeno- liths of the dark, dense agglomerate or pyroclastic rocks which determine their age as pre-batholithic. A few miles north of La Mesa, Hanna (i526, p. 200) has observed roof pendents of these older rocks surrounded by the quartz diorite.
In the region covered by the present report the agglomerates appear to occur in a band of varying width along the western margin of the quartz diorite batholith. This band extends from the north- eastern portion of the area mapped, in a south-southeasterly direction to and probably beyond the Mexican Boundary.
East of this band of old agglomerates and volcanics a quartz diorite batholith is the most im- portant country rock. This plutonic rock has intruded a considerable number of other rocks, some of which are schists which may have been ancient Paleozoic sediments. Fairbanks''’ gave an interesting account of the geology of the mountains of San Diego County in a report published by the California State Mineralogist in 1893. In his report, which includes a large number of field observations and determinations of igneous and crystalline metamorphic rocks, it appears that the region is a complex one petrographically. Fairbanks (1893, p. 116) mentioned the discovery in the Santa Ana Mountains of a gray limestone containing “fine specimens of a bivalve shell, and faint traces of corals and univalve shells” which were determined at the U. S. National Museum as of Carboniferous age. As pointed out by Hudson,''® these fossils probably came from Ladd Canyon and were the ones which J. P. Smith'”” once considered probably lower Triassic in age. Later Smith''® named the bivalve Daonella
112 In a recent paper, W. M. Davis (Proc. Nat. Acad. Sci., Vol. 18, no. 11, pp. 659-665, 8 text figs., Nov., 1932; Bull. Geol. Soc. Amer., Vol. 44, no. 5, pp. 1041-1133, 26 text figs., 16 pls., Oct., 1933) has given an interesting description of the marine terraces along the Malibu coast of Los Angeles and Ventura Counties, with a suggestion of a correspondence with the glacial chronology of the Sierra Nevada. Even if these terraces were due entirely to periodic eustatic changes in the level of the sea, which is not proved, their correspondence to terraces on other land blocks some distance away may be confused or entirely obscured by diastrophism in the second region. Lack of abundant fossils on these Quaternary terraces generally makes paleontologic correlations impossible. All the terraces in the Malibu region discussed by Davis are, in all probability, late Pleistocene and therefore they do not represent the major glacial sub-epochs of Pleistocene times.
113 Hanna, Marcus A., Univ. Calif. Publ. Bull. Dept. Geol. Sci., Vol. 16, no. 7, p. 203, 1926.
114 Mendenhall, W. C., U. S. Geol. Surv., Prof. Paper 71, p. 505, 1912.
115 Fairbanks, H. W., Calif. State Mining Bureau, 11th Ann. Rept. State Mineralogist, pp. 76-119, 1 map, 1893.
116 Hudson, F. S., Univ. Calif. Publ. Bull. Dept. Geol. Sci., Vol. 13, no 6, pp. 188-189, 1922.
117 Smith, J. P., Proc. Calif. Acad. Sci., Ser. 3, Vol. 1, p. 352, 1904.
118 Smith, J. P., U. S. Geol. Surv., Prof. Paper 83, p. 145, 1914. Daonella sanctae-anae Smith is figured on pl. 1, figs. 12-14. In regard to horizon and locality of this species, Smith stated (p. 145): “Rare in the Middle Triassic, near the head of Silverado Canyon (probably Bedford Canyon), Santa Ana Mountains, Orange County, Cal., associated with Rhynchonella sp. undt., and a rough-shelled ammonite not definitely determinable. Collected by H. W. Fairbanks.”
VotuME II] MarINE PLIOCENE OF SAN D1EGO, CALIFORNIA 33
sanctae-anae and, presumably due to the apparent close relationship of this new species to Daonella béckhi Mojsisovics of the middle Trias of the Alpine Province, he referred the beds from which this species was collected to the middle Triassic. In the meantime Stanton had concluded that the Ladd Canyon fossils could be taken to “clearly indicate the Triassic age of the fauna,” which he believed was “probably upper Triassic rather than older.” The importance of the age determination of these Santa Ana Mountains schists and associated limestone’? is that they appear to be equivalent to some of the metasedimentary rocks of the mountains further south in San Diego County, as early suspected by Fairbanks.
Hudson’”’ has contributed an important paper on the crystalline rocks of the Cuyamaca region in San Diego County. This paper was a result of his study of the gold deposits which had been mined there. He states (p. 181) : “The rocks exposed at the surface over a large part of the mountainous region of San Diego County are quartz-bearing plutonic rocks, varying from quartz diorite to true granite in composition. The relation of these rocks to the older rocks which they have intruded shows that the intrusion was of batholithic nature. Most of the cover has been stripped from this batholith, the older rocks being found as remnants, surrounded by granite. These older rocks are schists, the result of metamorphism of shales and sandstones, with subordinate layers of lava.” In the Cuyamaca region Hudson reports the occurrence of basic plutonic rocks, such as basic diorite, gabbro and norite, as well as pegmatites which, in parts of San Diego County, are important sources of gem minerals such as Tourmaline, Kunzite, Beryl, etc. In regard to the date of intrusion of the quartz diorite Hudson states: “The quartz-diorite batholith was developed in post-Triassic time and is probably equivalent to the post-Mariposa intrusions of the Sierra Nevada.”
A number of short papers have appeared from time to time bearing on minerals or special rock types occurring in San Diego County. Among them may be mentioned papers by Lawson, Schaller and others. References to these papers may be readily found in the various bibliographies by Nickles'*! and Shedd.'** An excellent brief summary of the crystalline rocks of San Diego County appears in an important work by Reed'” on the geology of California. More recently Miller'’* briefly described the geology of a section across a portion of San Diego County. In this paper he described principally the igneous and metamorphic rocks observed in an area contiguous to the highway through La Mesa, Descanso, Jacumba to just beyond Mountain Springs in Imperial County.
Igneous rocks are rare in the coastal region of San Diego County. However, it is of interest to note that Blake'” reported the presence of a dike of greenstone along the southeast side near the southern end of Point Loma. Although we have not seen this dike we believe the sedimentary beds cut by the intrusion are of Cretaceous age. A basaltic dike said to be from two to thirty feet thick occurs about a quarter of a mile north of the pier of the Scripps Institution of Oceanography and about 214 miles north of La Jolla. It cuts the Rose Canyon shale and is exposed along the beach but does not extend to the top of the high bluff. It is the only igneous intrusion in the Eocene of which we are aware in this region. It has been described by Fairbanks'*® and by M. A. Hanna.'”” The only
119 H. W. Hoots (U. S. Geol. Surv., Prof. Paper 165-c, pp. 88-89, 1931) referred the Santa Monica slate of the eastern part of the Santa Monica Mountains (Los Angeles County) questionably to the Triassic, “in view of its similarity to the fossiliferous Triassic slate of the Santa Ana Mountains, both in lithologic character and in its relations to fossiliferous Cretaceous rocks and an earlier granitic intrusion.” It might be mentioned that the Santa Monica slate, which is a formation characterized chiefly by its total lack of recognizable fossils and its rock cleavage parallel to the original bedding planes, bears considerable resemblance to some phases of the Franciscan formation of the coast ranges of middle and northern California (probably of Jurassic age in part) and likewise to some statically metamorphosed argillites and phyllites, with cleavage parallel to the bedding planes, occurring in parts of the Mojave Desert and, by their geologic relations, believed to be of pre-Cambrian age. The similarity of these latter mentioned rocks was called to our attention by Professor A. R. Whitman.
120 Hudson, F. S., Univ. Calif. Publ. Bull. Dept. Geol. Sci., Vol. 13, no. 6, pp. 175-252, 7 text figs., 1 map, pls. 9-14, June 29, 1922.
121 Nickles, J. M., U. S. Geol. Surv., Bull. 746, 1923; Bull. 747, 1924; Bull. 823, 1931.
oe Hi Shedd, S., State of California, Dept. Nat. Resources, Division of Mines, Geologic Branch, Bull. 104, 1933; Bull. GEE Reed, R. D., “Geology of California,” published by the Amer. Assoc. Petrol. Geol., Tulsa, Oklahoma, May, 1933.
124 Miller, W. J., “A Geologic Section Across the Southern Peninsular Range of California,” Calif. Journ. Mines and Geology, Vol. 31, no. 2, (31st Rept. State Mineralogist), pp. 115-142, 8 text figs., 1 plate (geologic map and sections), 1935.
125 Blake, W. P., U.S. Pacific R. R. Repts., Vol. 5, p. 176, 1856. 126 Fairbanks, H. W., 11th Ann. Rept. Calif. State Mineralogist, pp. 96-97, 1893. 127 Hanna, M. A., Univ. Calif. Publ. Bull. Dept. Geol. Sci., Vol. 16, no. 7, p. 224, 1926.
34 San Dreco Society OF NatTuraL History {Memoirs
indication in this region of igneous activity during Eocene time is the rare occurrence of ash beds in the Poway conglomerate. The occurrence of bentonite in this region is mentioned in the discussion of the Pliocene sediments in the present paper.
During the course of the field work in this area, the authors collected a number of hand specimens of rock from the granitic batholith and from the volcanics and agglomerates to the east of the Pliocene beds. Thin sections of twelve of these specimens were made by Hochgesang and Vogel in Goettingen, Germany. The hand specimens were studied by the late Dr. John E. Wolff of Pasadena, California, and the thin sections were studied by Dr. Wolff and by Dr. Gordon A. Macdonald whose reports
are included here. Their names accompany the descriptions which each has furnished.
No. 1. From south side of Sweetwater Dam, close to the upper part of the dam:
Hanp Specimen. Dark gray, dense, breccia, the rock fragments even smaller than in No. 2.
Section. The rock fragments are the same as those of Nos. 2 and 3, i.e., fine-grained feldspar or quartz feldspar lavas, often graphic, but one is a fine-grained granite porphyry, with phenocrysts of quartz and feldspar in a microgranitic groundmass, and another is perhaps a silicified tuff from the same rocks. The cement has broken fragments of the same rocks, quartz feldspar, occasional fragments of ferromagnesian minerals now re- placed by epidote, calcite and iron ore; large areas of calcite and epidote, the base of the cement, as before, fine silica grains and sericite. (J. E.Wolff).
No. 2. From foundation rock of Sweetwater Dam, taken from north side, 6 to 9 feet from the top of the concrete work. This rock weathers light buff gray or becomes stained brownish red from iron oxide.
Hanp Specimen. A dense dark gray breccia, with small fragments of rock, biotite or chlorite, and frequent small masses of pyrite.
Section. Finer-grained than No. 3. The rock fragments are smaller, but essentially the same, of fine- grained quartz feldspar graphic inter-growths, with occasional phenocrysts of orthoclase and plagioclase. The cement again essentially a fine-grained quartz aggregate and plates of sericite, with broken feldspar (orthoclase and acid plagioclase fragments), pyrite and magnetite areas, much epidote, sericite, etc., in the altered feldspars; chlorite, clastic augite, sometimes replaced by uralite, calcite, quartz fragments. (J. E. Wolff).
No. 3. Breccia from south side of upper Las Choyas Valley, just south of the V in valley:
Hanp Specimen. Small fragments of feldspar, etc., in a dark gray, quartzitic groundmass.
Section. A number of large and small rock fragments in a cement. The rock fragments are largely of fine- grained igneous rocks, having fine feldspar laths in flow structure, with or without quartz between. Some seem identical with the alaskite-porphyry, below, others are pure feldspar, a plagioclase too fine to determine, one of fine-grained biotite granite, and others composed of fine interlocking quartz grains, a quartzite or chert, others contain larger angular grains of quartz and feldspar in the same fine quartz aggregate—a silicified arkose or tuff. Also a limonitized limestone. The cement of the tuff has small similar rock fragments, fragments of quartz and feldspar, much epidote, chlorite, limonite and so forth, the ultimate cementing material minute grains of quartz
and sericite. (J. E. Wolff).
No. 4. Rock samples from west side of Lower Otay Dam:
Hanp Specimen. A dense dark gray flinty rock, through which ill-defined and evidently altered feldspar phenocrysts are scattered.
Section. The feldspar phenocrysts are orthoclase and a plagioclase probably albite, much decomposed, with epidote, quartz, calcite as products. One or two bunches of secondary green hornblende may represent original augite. The groundmass has small slender feldspars, largely albite-oligoclase, probably orthoclase, with quartz filling, and decomposition products. The rock is probably identical with No. 8, but much changed, i.e., an alaskite-porphyry. (J. E. Wolff).
No. 5. Sample from hillside about 1 mile west of Sweetwater Dam:
Hanp Specimen. Dense dark gray with little pyrite areas common and small phenocrysts of feldspar.
Section. Large phenocrysts of colorless augite, largely replaced by epidote aggregates, and of basic oligoclase, also epidotized. The groundmass is composed of small laths of oligoclase, scattered in what was once a glass, now a mass of granular decomposition products. The rock is probably an augite-andesite? (J. E. Wolff).
No. 6. One-half mile southwest of Grossmont High School, on north slope of Grossmont, just above foot of the mountain: Hanp Specimen. A coarse-grained, feldspar-rich and hornblende-poor rock, containing patches of a finer-
grained more basic feldspar-hornblende rock, in which a rough ratio is two hornblende to three feldspar. (J. E. Wolff).
Votume II) MariINE PLIOCENE OF SAN DIEGO, CALIFORNIA 35
Section. Coarse-grained facies: Hypidiomorphic texture. Plagioclase is the most abundant constituent, and shows well-developed zoning, from acid labradorite in the center to oligoclase on the outside. Intersticial quartz is abundant. The ferromagnesian minerals are green hornblende and less abundant brown biotite. Minor accessory minerals include abundant magnetite, less abundant apatite and titanite, and a few crystals of zircon.
Fine-grained facies: A basic inclusion, composed of the same minerals as the coarse-grained rock, but with a greater percentage of dark minerals, and a smaller amount of biotite in relation to hornblende. A little orthoclase is also present, as large crystals carrying poikilitic inclusions of andesine and hornblende.
The rock is a hornblende-biotite quartz diorite, containing basic inclusions of schlieren. In the San Luis Rey quadrangle just to the north, Hurlbut (Amer. Mineralogist, Vol 20, pp. 609-630, 1935) considers the dark schlieren to have been derived by reaction of the quartz diorite with xenoliths of the older San Marcos gabbro. (G. A. Macdonald).
No. 7. West slope of Grossmont, about one-half way up, just east of La Mesa:
Hanp Specimen. Fine-grained pinkish biotite-granite. Scattered feldspars are decomposed to limonite. (J. E. Wolff).
Section. The texture is hypidiomorphic. Essential minerals are orthoclase and quartz, with a little micro- cline, and a subordinate amount of oligoclase. The ferromagnesian mineral is brown biotite. Accessory minerals include magnetite, apatite, titanite, and zircon, the latter enclosed in the biotite and surrounded by pleochroic halos. The biotite is in subhedral plates, and the oligoclase varies from subhedral to nearly euhedral in outline. Orthoclase varies from subhedral to anhedral. The quartz was clearly the last mineral to crystallize, occurring as anhedral grains intersticial to the other components. The rock is slightly altered; the orthoclase shows traces of kaolinization, and a few of the biotite flakes are partly changed to chlorite.
The rock is a biotite granite. (G. A. Macdonald).
No.8. First hard rock outcrop on hillside, east margin of Otay Mesa, at east end of main east- west road:
Hanp Specimen. A lighter gray and coarser rock than No. 9; numerous small phenocrysts of feldspar. Limonitized pyrite grains. (J. E. Wolff).
Section. Porphyritic, with phenocrysts of albite in a groundmass composed of small laths of albite and intersticial quartz. Small, irregular areas of epidote, chlorite, and calcite are scattered through the slide. A little magnetite is present.
The larger phenocrysts, which Wolff identified as orthoclase, show a positive sign, with 2V about 75° and an index lower than balsam, and are certainly albite.
The rock is an albitite. (G. A. Macdonald).
No. 9. From north slope of 667 foot hill, north side of Otay Valley about 314 miles west from lower Otay Dam:
Hanp Specimen. A dark gray, fine-grained rock, showing small crystals of feldspar, small specks of pyrite common, and large vein-like or concretionary masses of pyrite, quartz and a white granular mineral. (J. E. Wolff).
Section. The rock is very much altered, but I believe it represents a propylitized andesite. Phenocrysts of some femic mineral, probably augite, have been changed to epidote and chlorite. The feldspars have been saus- suritized, and are now represented by mixtures of albite, epidote, chlorite and calcite. There are also present abundant fine, irregular grains of iron ore, some of them no doubt original, but many being separated out during the change of the femic minerals to chlorite, with which they are closely associated. (G. A. Macdonald).
No. 10. About 300 yards east of Isham Springs, Sweetwater Reservoir :
Hanp Specimen. A dark flinty rock with irregular pinkish-white areas evenly distributed in a dark gray groundmass.
Section. The rock is mainly composed of a fine, interlocking aggregate of quartz grains, in which are scattered fragmentary crystals of larger size feldspars, mostly andesine, also patches of muscovite or chlorite plates, little grains of ore, often with associated rutile crystals, much epidote. The feldspars are clastic, the rest meta- morphic, an altered sediment, perhaps a tuff. (J. E. Wolff).
No. 11. About 34 mile north of Aloha, edge of mesa, north of Sweetwater Valley:
Hanp Specimen. Dark gray, fine-grained basaltic rock, small phenocrysts of feldspar.
Secrion. Small phenocrysts of a very basic labradorite (bytownite) are common, and a few of augite. The groundmass is composed of similar feldspars in flow structure, and small grains of augite and magnetite, with perhaps a very little interstitial glass here and there. Epidote, chlorite and other alteration products. The rock is a feldspar basalt. (J. E. Wolff).
No. 12. In road pass about 114 miles east of summit of Mount Helix:
a Tia Specimen. A fine-grained, biotite-rich, granitic rock; the feldspars have a slight lilac color. (J. E. olf).
36 San Disco Society oF Natura History [Memotrs
Secon. Hypidiomorphic texture. Essential minerals are andesine, orthoclase, and quartz. The andesine shows distinct zoning, varying from intermediate andesine (An,,) in the center to acid andesine (An,,) on the outside. The andesine is much more abundant than the orthoclase. Ferromagnesian minerals include green hornblende and brown biotite, in part intergrown. Many of the hornblendes contain a central core of diopsidic augite, the c crystallographic axis in the augite being parallel to that in the enclosing hornblende. The properties of the augite are: (+-)2V = 60°, very weak, Z c = 40°. Minor accessories are magnetite, apatite, zircon, and titanite. Some of the biotite is slightly chloritized.
The rock is a hornblende-biotite quartz diorite. Wolff’s designation of the rock as a granodiorite seems to me undesirable, since a granodiorite should contain about half as much orthoclase as it does plagioclase, while this rock carries very much more abundant plagioclase than it does orthoclase. (G. A. Macdonald).
No. 13. Igneous rock outcropping 14 mile north of Aloha and 5 mile W-NW of Sweetwater
Hanp Specimen. The rock is a fine-grained, dense, greenish-gray basalt.
Section. Microscopically, it consists of phenocrysts of labradorite and diopside in a pilotaxitic groundmass of labradorite laths and grains of serpentinized diopside, with abundant small grains of magnetite. The feldspar phenocrysts are slightly zoned, varying from medium labradorite in the center to acid labradorite on the edges. Some oscillatory zoning is present. The feldspar microlites in the groundmass are acid labradorite. Diopside is very largely altered to serpentine, usually showing a net structure; but a few grains of diopside remain un- altered. (G. A. Macdonald).
Of these rock specimens Nos. 6, 7 and 12 are from the granitic batholith, while the others are from the volcanics and agglomerates. Nos. 1, 2 and 3 appear to be much altered tuffs, probably originally of andesitic nature. Nos. 4 and 8 are albitite, Nos. 5 and 9 altered augite andesites, No. 6 a quartz diorite, No. 7 a biotite granite, No. 10 probably a tuff, Nos. 11 and 13 are basalts, and No. 12 a diorite.
CRETACEOUS
Marine beds of Cretaceous age which underlie the Eocene in the area under discussion are exposed at only a few places. They are found principally near the coast, due to the fact that the Eocene strata over most of the area have not been elevated sufficiently to permit recent erosion to cut through to the lower beds. In the La Jolla Quadrangle, M. A. Hanna’’® discussed the Cretaceous deposits which are exposed along the coast from about one-half mile north of False Point to north of the City of La Jolla, and also on the north slope of Mount Soledad. These beds, which were referred to the Chico, upper Cretaceous age, are about 500 feet thick and consist of shales and sandstones of varying hardness. The Cretaceous sandstones forming the terrace upon which La Jolla has been built are resistant to erosion, but joints, faults and irregular induration have permitted wave action to produce numerous caves and small coves due to the more rapid removal of the softer material. Eocene rocks unconformably overlie the Cretaceous beds in that area.
Farther south, on the west side of Point Loma from west of the Theosophical Institute up to and including the southern point of the peninsula, Cretaceous shales and sandstones are well exposed close to the water’s edge. Fairbanks’’’ briefly discussed the geology of Point Loma and referred briefly to these Cretaceous beds. He assigned the beds at the southern end of Point Loma to the Chico, upper Cretaceous, but supposed the heavy overlying conglomerates to be of late Tertiary age,'*® whereas it seems more probable that they belong to the upper Eocene. They apparently unconformably overlie the Cretaceous strata.
At the extreme south end of Point Loma, a thin-bedded bluish gray shale occurs at the base of the cliff. ‘These strata are well exposed for over a hundred yards east of the small cave near the lighthouse. The dip of these beds is about 11° toward the east, and they soon disappear beneath the rocky beach. In these shales the authors collected a few specimens of Baculites and fossils of a plant identified by Dr. L. M. Waitzinger as a conifer of ancient type. From this locality (Loc. 1173 C.A.S.)
128 Hanna, M. A., Univ. Calif. Publ. Bull. Dept. Geol. Sci., Vol. 16, no. 7, pp. 205-207, 1926. — See also, Hertlein, L. G., and Grant, tv, U. S., Calif. Journ. Mines and Geol., Vol. 35, no. 1. 35th Rept. Calif. State Mineralogist, pp. 62-65, Jan., 1939 [received at library of the California Academy of Sciences, Aug. 23, 1939].
129 Fairbanks, H. W., Calif. State Mining Bureau, 11th Ann. Rept. Calif. State Mineralogist, pp. 94-96, 1893.
130 Fairbanks (1893, p. 96), however, did report the occurrence of Eocene fossils in the low bluffs at the northeast end of Point Loma.
VotumE IT] Marine PLIOCENE OF SAN D1EGO, CALIFORNIA 37
Mr. C. C. Church, paleontologist with the Tidewater Associated Oil Company, has identified fora- minifera in a sample of dark gray shale. He has submitted to us the following report on these foraminifera :
The foraminifera listed here were concentrated from gray shale collected by Dr. L. G. Hertlein in September, 1928. The preservation is good but the total number of specimens recovered is small. For the number of specimens the list of genera is relatively short. The species are as follows:
Anomalina sp.
Allomorphina cf. minuta Cushman
Bulimina obtusa d’Orbigny
Globotruncana arca Cushman
Gyroidina sp.
Gaudryina (Pseudogaudryina) pyramidata Cushman Gaudryina oxycona Reuss
Marginulina humilis Reuss
Robulus sp.
Spiroplectammina anceps Reuss
These foraminifera are commonly found near the middle of the upper Cretaceous, that is, below the Moreno and probably in the upper half of the Panoche group of F. M. Anderson.
The Eocene beds overlying the Cretaceous at Point Loma are composed of sandstones and con- glomerate. These Eocene beds at one place near the point dip about 30° to the east-southeast. Boulders made up of sandstone are present, and near the top huge boulders occur which apparently came from the crystalline rocks many miles to the east. Both the Cretaceous and Eocene are cut by faults.
A number of species have been listed from the Cretaceous of Point Loma by Cooper’*! and Anderson.” The published lists of the species from that locality are in need of revision, as some of the species cited are now known to occur in the Eocene or at other localities in the Cretaceous and not at Point Loma.
The list here given has been compiled from published lists and from collections in the California Academy of Sciences.
BRACHIOPODA “Waldheimia” imbricata Cooper
PELECYPODA Acila demessa Finlay Coralliochama orcutti White Crassatellites lomana Cooper (type locality) Cymbophora ashburnerii Gabb Glycymeris veatchii Gabb Inoceramus sp. Lima appressa Gabb Nemodon vancouverensis Meek Opis triangulata Cooper (type locality) Pholadomya brewerii Gabb Protocardium placerensis Gabb Tellina decurtata Gabb Tellina whitneyi Gabb Trapezium carinatum Gabb Trigonocallista varians Gabb
GASTROPODA Acteonina pupoides Gabb Cerithium pillingi White Gyrodes conradiana Gabb Haliotis lomaénsis Anderson (type locality) Oligoptycha obliqua Gabb Patella cf. traskii Gabb
131 Cooper, J. G., Calif. State Mining Bureau, Bull. 4, pt. 5, pp. 60-63, 1894. See also, Cooper, A. S., Calif. State Min. Bur., Cat. State Mus. Calif., (Sacramento), Vol. 5, pp. 118-122, 1899. 132 Anderson, F. M., Proc. Calif. Acad. Sci., Ser. 3, Geology, Vol. 2, no. 1, pp. 27-32, 1902.
38 San Dreco Society oF NaTuraL History {[Memorrs
CEPHALOPODA Baculites fairbanksi Anderson Hamites vancouverensis Meek Heteroceras cooperii Gabb (type locality)
Parapachydiscus catarinae Hanna and Anderson
This assemblage indicates an upper Cretaceous age, probably Campanian, upper Senonian.
Mr. Frank Stephens and Mr. Cecil V. Robinson discovered a new Cretaceous fossil locality near the southern end of Point Loma which has yielded specimens of Parapachydiscus catarinae Hanna and Anderson,'**? Coralliochama orcutti White,'** Volutoderma gabbi White, Inoceramus sp. and other mollusks. The Parapachydiscus and the Coralliochama also occur in the northern district of Lower California, the Parapachydiscus in the Santa Catarina region and the Coralliochama at Punta Banda, Lower California, Mexico. The Parapachydiscus also occurs in the upper Cretaceous north of Coalinga, Fresno County, California. These occurrences indicate that this Parapachydiscus zone is of considerable importance for purposes of correlation.
A well drilled by the Borderland Exploration Company on Point Loma gives some definite data on the thickness of the Cretaceous beds at that locality. This well, which was known as Point Loma No. 1, was located on Pueblo Lot No. 211, section 30, Township 16 South, Range 3 West, San Bernardino Base and Meridian, and was drilled to a depth of 5,101 feet. The log furnished through the courtesy of G. D. Hanna and C. C. Church is as follows:
1,560 feet. Core. Hard gray sandy shale; plant fragments.
1,580 feet. Core. Hard gray sandy shale; plant fragments, foraminifera, fragments of Inoceramus and ammonites.
1,680 feet. Core. Hard gray sandy shale; plant fragments and ammonite fragments.
1,787 feet. Core. Hard gray sandy shale; plant fragments.
1,885 feet. Core. Hard gray sandy shale; plant fragments.
1,945 feet. Core. Hard gray sandy shale; fragments of Baculites chicoensis Trask.
2,000 feet. Core. Hard gray silty clay shale; foraminifera rare and small, Textularia, Silicosigmolina, Mar- ginulina. Foraminifera in core appear to be Cretaceous, but determination not certain.
2,010 feet. Core. Hard gray sandy shale; plant fragments.
2,100 feet. Core. Coarse greenish pebbly sandstone.
2,250 feet. Bit. Gray fine to coarse sand and shale; no fossils.
2,500 feet. Core. Hard gray sandy shale; plant fragments, foraminifera and a large piece of an ammonite.
2,771 feet. Core. Hard reddish brown sandstone with pebbles; marked “top of red beds.”
3,110 feet. Core. Hard red sandstone.
3,670 feet. Core. Hard red conglomerate; pebbles up to 3 inches. All samples with fossils are Cretaceous. The red beds are of uncertain age; nothing similar to this in West Coast Cretaceous, so may be older.
3,735 feet. Core. Hard greenish-gray altered rock, probably metamorphosed rhyolite or similar form. In thin flakes under the microscope the substance is seen to be translucent. It contains no sand or quartz and does not belong to the granite series. Pyrite and calcite are found in seams and the rock itself contains some mineral which reacts like dolomite in hot acid, although the proportion is small.
3,828 feet. Core. Greenish-gray, partially crystalline, limy, altered rock with veinlets.
3,857-58 feet. Core. Brown loose fine sand; no fossils. The brown sand of the last sample is so loose as to seem out of place with the dense limy rock a few feet above it. No fossils were noted to indicate the possible age of the material.
133 Hanna, G. D., and Anderson, F. M., Pan-American Geologist, Vol. 50, no. 4, p. 283, pl. 9 (larger shells in the illustration), Nov., 1928. Name and figure only. “. .. from a few miles southwest of Santa Catarina, and from the uppermost beds of the Cretacic section exposed there.” Lower California. — Anderson and Hanna, Proc. Calif. Acad. Sci., Ser. 4, Vol. 23, no. 1, p. 19, pl. 1, fig. 1, pl. 2, fig. 1, pl. 3, figs. 1-3, Dec. 23, 1935. “Near Santa Catarina Landing, Lower California.” Upper Senonian, upper Cretaceous. — Johnson, M. E., “West Coast Shells,” (Edwards Brothers, Inc., Ann Arbor, Michigan), 1937, p. 38, fig. 114 (figure at right). Near Catarina, Lower California.
134 For references to Coralliochama orcutti White see Anderson, F. M., and Hanna, G. D., Proc. Calif. Acad. Sci., Ser. 4, Vol. 23, no. 1, p. 31, 1935. Definitely recorded from Point Loma and La Jolla, Calif. H. W. Fairbanks (1893, pp. 95, 96) recorded the species from the same localities, and Stearns (Science, New Ser., Vol. 12, no. 294, p. 248, Aug. 17, 1900), also recorded the species from La Jolla.
Rudistids are comparatively rare in the Cretaceous of western North America. Packard and Lupher have described two rudistids, one from the Jurassic, and one from the Cretaceous of Oregon (Univ. Oregon Publ. Geol. Ser., Vol. 1, no. 3, pp. 203-212, 6 pls., issued Dec. 30, 1929), Orcutt stated (Jamaica Nat., Vol. 1, no. 1, 1927, p. 3), that the genus Coralliochama had been reported from Washington.
VotumE II] MarINE PLIOCENE OF SAN DIEGO, CALIFORNIA 39
4,290 feet. Core. Light gray, hard, fine-grained crystalline rock with seams of calcite. This confirms the
determination made higher in the well that the formation is non-sedimentary.
This well was drilled to 5,101 feet, where brownish gray shale and sandstone were logged.
From this log it appears that the marine Cretaceous beds (“Chico”) at this locality are not more than 1,211 feet thick. If the red beds (964 feet) are non-marine Cretaceous, as seems likely, then the total thickness of the Cretaceous here is not more than 2,175 feet.
The log of the Holderness well, near the mouth of the Tia Juana River, given in a later part of the present paper (page 59) shows that the marine Cretaceous is not more than 1,360 feet thick in that area. The underlying red beds,'”” 269 feet thick, may be non-marine Cretaceous, in which case the total thickness of Cretaceous beds in that area would be 1,629 feet. The dip of the beds penetrated by the wells is unknown to us and therefore their exact maximum stratigraphic thickness is unknown.
Information from Mr. Donuil Hillis, geologist with the Capital Company, San Francisco, and Dr. A. L. Tull, San Diego, on Capital No. 1 Well was recently made available to us. This well is stated to be “150 feet east and 547 feet north of the southwest corner of Pueblo Lot 1237, which would be in the Projected Section 32, of Township 15 South, Range 3 West” (Hillis). According to Mr. Hillis (letter to U. S. Grant, 1v, dated at San Francisco, September 11, 1942), Dr. Tull believed the Cretaceous was encountered at a depth of 4,400 feet and the well was still in rocks of that age at 6,130 feet. The data supplied by Mr. Hillis and Dr. Tull indicate a considerably greater thickness of both Eocene and Cretaceous than that known from the outcrop sections. Due to the fact that the Cretaceous lies upon an uneven erosion surface it is likely that thicknesses will vary considerably. This well is near Rose Canyon, where folding along the Soledad anticline might give a somewhat exaggerated stratigraphic section in a well.
The following additional information on Capital No. 1 Well was provided by Mr. Charles H. Reed, Secretary-Engineer, Bureau of Mines of San Diego County, in oral statements to Mr, Clinton G. Abbott on March 3, 1943, and a letter to him on April 30, 1943. The formations encountered in drilling were entirely sedimentary. The ultimate depth of 6,130 feet is deeper than any other well ever drilled in San Diego County except one at Imperial Beach, which struck salt water at 6,400 feet. On March 3, 1943, there were 850 feet of fluid in the bottom of Capital No. 1 Well, of which 30% was water and 70% was oil of 24.8 gravity. The temperature of the water was 168°F. Mr. Reed believed that strata producing oil and gas were penetrated by the well between the depths of 5,904 and 6,130 feet. He further stated that drilling was suspended about the latter part of August, 1942, and that, due to mechanical difficulties, it was impossible to drill the well deeper.
Many years ago a vertical shaft was sunk to a depth of about 125 feet on the terrace on the west side of Point Loma, approximately one and three-fourths miles north of the present lighthouse, in search of coal.!2° It is said that several strata of coal were penetrated, one of them being five feet thick and having a dip toward the east.'? Although we visited the entrance to this shaft we were
135 These red beds may be a southern extension of the Trabuco formation in the Santa Ana Mountains, Orange County, Calif. This formation was named by E. L. Packard, Univ. Calif. Publ. Bull. Dept. Geol. Sci., Vol. 9, no. 12, p. 140, Feb. 8, 1916. See also, Popenoe, W. P., Journ. Geol., Vol. 49, no. 7, pp. 738-752, 1941.
The red conglomerate resting on the diorite at Punta Banda, on the south shore of Todos Santos Bay, about seventy-five miles south of the United States-Mexico Boundary, may likewise represent the Trabuco formation. At that locality the fossiliferous Cretaceous is in fault contact with the red beds.
136 The San Diego Herald (Vol. 5, Nov. 24, 1855, p. 2, col. 1), stated that coal was discovered by Ladd, Green, Tanner and Serrine on the shore of the Pacific about two miles north of Point Loma. It was tested and found to burn with a clear flame, and gave off intense heat. The following year the same paper (Vol. 5, Feb. 2, 1856, p. 2, col. 2), stated that the company had bored 45 feet and passed through 10 or 12 different strata of coal, which varied from three inches to one foot in thickness.
Smythe wrote regarding this mine as follows:
“One of the most interesting episodes of the early days was the work of some Mormons, bent upon the enterprise of mining coal on the north [west] shore of Point Loma, late in 1855, in response to a ‘revelation.’ Obtaining a lease of land from the city trustees they proceeded to make borings which penetrated several strata of coal, ranging from three inches to a foot in thickness. In April, 1856, they announced that they had discovered a vein of good coal four and a half feet thick near the old lighthouse on Point Loma, and began to sink a shaft. Considerable machinery was installed and a few experienced miners, as well as engineers, employed, but nothing came of the enterprise.” See Smythe, William E., “History of San Diego,” (The History Co., San Diego, Calif., 1907), pp. 259-260.
A modern account of the history of this mine by Winifred Davidson (Mrs. John Davidson), occurs in the San Diego Union, second section, Sunday Morning, Jan. 31, 1932, p. 2, col. 4, 1 illustration.
137 San Diego Herald, June 28, 1856, p. 2, col. 1.
40 San Disco Society oF Natura History [Memorrs
unable to determine whether the coal was of Eocene or Cretaceous age. That this shaft penetrated beds of Cretaceous age, however, is certain since Gabb described “Ammonites” cooperii, an upper Cretaceous form, “from a shaft sunk in search of coal on the west side of Point Loma, opposite La Playa, San Diego.”'*® A map’”’ by C. B. Wadleigh published in 1888 bears the words “Coal measures” in the ocean off this part of Point Loma.
A few miles farther north, coal was encountered in a boring at La Jolla which Fairbanks (1893, p. 96) said must be Cretaceous in age. Cretaceous rocks are exposed there, but we have no later infor- mation on the occurrence of this coal.
Blake reported the presence of a dike of greenstone along the southeast side of Point Loma. We did not investigate this dike, but we believe that it cuts Cretaceous sediments. Another dike occurs near the Scripps Institution of Oceanography north of La Jolla and cuts the Eocene rocks there.
EOCENE In his report on the geology of the La Jolla Quadrangle Marcus Hanna’ briefly reviewed the
literature on that area and gave a complete list of references. Hanna’s paper is the most complete report yet published on the Eocene in the area immediately north of the San Diego Pliocene basin and the reader is referred to it for details which need not be repeated here. The following table, taken without change from Hanna’s report on the paleontology of the La Jolla Quadrangle, is an excellent summary of his treatment of the stratigraphy:
Thickness Pliocene, San Diego formation in feet Unconformity § Massive conglomerate, boulders well rounded, largely porphyritic vol- c- ; 3 & | Poway con- canics; coarse; cross-bedded yellow and brown sands; some fine & £ ] glomerate shaly sands with partings well developed due to mica; upper part ie contains considerable soft white caliche.....0.0.0.0.000.0200.cceeeseeeeeeee 1000
Unconformity, at least in part.
g Light gray mudstone, slightly laminated in places; gray and yellow
3 & | Rose Cafion sandy shale; yellow and brown sands; in upper part lenses of con- ‘& shale glomerate, boulders well rounded, largely porphyritic volcanics, E but some of the underlying mudstones and sands..............-.--...-.---- 300 3 A + d Massive, white, coarse-grained, cross-bedded sand, arkosic and some- aia times carrying much muscovite and biotite.................0:sscesessseseeeeeees 20-200 Sires sand Greenish, gray, purple, red sands and sandy shale; some thin beds
composed almost wholly of Ostrea idriaensis Gabb.............2....000.- 100
Unconformity Cretaceous, Chico formation
Neither the Delmar sand nor the Torrey sand appear to be exposed in the San Diego Pliocene basin southeast of Mission or False Bay, but they are well exposed in parts of the La Jolla Quadrangle to the north. The base of the Delmar sand is nowhere exposed in the area studied by Hanna though it is possible it may be exposed farther north and its equivalent may outcrop along the shore just north
138°2A[mmonites]. Cooperii, n.s.” Gabb, Geol. Surv. Calif., Palaeo., Vol. 1, p. 69, pl. 14, figs. 23, 23a, 1864. This species is referable to some genus with ornamentation similar to that of Anisoceras Pictet.
139 Wadleigh’s Map of the City of San Diego, San Diego County, Calif. C. B. Wadleigh, Publisher, 913 Fifth Street. Scale 4 inches to the mile. Copyrighted 1888. Lith. by Los Angeles Lith. Co., 48 and 52 Banning Street, Los Angeles, Calif. This map was called to our attention by Mr. John Davidson, Curator of the Junipero Serra Museum, San Diego Historical Society.
140 Hanna, M. A., “Geology of the La Jolla Quadrangle, California,” Univ. Calif. Publ. Bull. Dept. Geol. Sci., Vol. 16, no. 7, pp. 187-246, pls. 17-23, 1 map, Nov. 20, 1926. See especially pp. 189-191. The paleontology of the Eocene of this quadrangle by the same author is entitled “An Eocene Invertebrate Fauna from the La Jolla Quadrangle, California,” and is no. 8 in the same bulletin, pp. 247-398, pls. 24-57, March 25, 1927. — See also, Cushman, J. A., and Hanna, M., “Foraminifera from the Eocene near San Diego, California,” Trans. San Diego Soc. Nat. Hist., Vol. 5, no. 4, pp. 45-64, pls. 4-6, March 15, 1927. — See also, Hertlein, L. G., and Grant, tv, U. S., Calif. Journ. Mines and Geol., Vol. 35, no. 1, 35th Rept. Calif. State Mineralogist, pp. 65-68, Jan., 1939 [received at library of the California Academy of Sciences, Aug. 23, 1939].
VotuMmE IT] MarINE PLIOCENE OF SAN DIEGO, CALIFORNIA 41
of the Pacific Beach Pliocene section where it overlies the Cretaceous. As pointed out by Hanna,'*! this lowest member of the La Jolla formation was apparently deposited in a shallow brackish water embayment. The most common species, Ostrea idriaensis Gabb, Potamides carbonicola Cooper and Unio (?) torreyensis M. A. Hanna, together with mud-flat sediments alternating with cross-bedded and rapidly lensing layers, are features confirming Hanna’s opinion. The peculiar greenish hue of much of the Delmar is also similar to certain other known brackish water deposits. This brackish water facies is most prominent towards the top of the Delmar where layers of fossil leaves are occasion- ally found. In the lower part of the formation as exposed, particularly along the beach at the foot of Torrey Pines Grade, the sediments have a more normal marine facies. It is in these more normal marine lower beds that most of the 32 species listed by Hanna occur. According to Hanna, “With the exception of four species, all of the 32 species determined from the Delmar sand were present in the Rose Cafion shale. These four species were not found to be abundant in the Delmar sand. Because of these data it is believed the Delmar sand and the Rose Cafion shale constitute a unit faunally, although a difference in salinity of the water and possibly a period of elevation separated the deposition of the two, as is shown by the Torrey sand.” The preservation of the Delmar fossils is on the whole very poor and the total fauna is no doubt much larger than the 32 species determined by Hanna. Recent detailed studies of the Eocene, chiefly by Mr. Frank B. Tolman and by Professor B. L. Clark and his students, have shown that it is possible to recognize a larger number of faunal horizons than was known at the time Hanna’s paper was published, and on the basis of these recent data, the Delmar would be differentiated faunally from the Rose Canyon shale faunas.
When in superposition the Torrey sand is in gradational contact with the underlying Delmar. However, in at least one place, the Torrey sand is seen to rest with marked unconformity on the Black Mountain volcanics, indicating an overlap of the Delmar by the Torrey to the east. It is well exposed sometimes in castellated erosional'*? remnants high up on the hillsides in the general vicinity of the mouth of Soledad Canyon south of Del Mar.
While not explicitly stated by Marcus Hanna, the Torrey sand, from its coarse-grained, cross- bedded, and sometimes reddish colored character, together with the almost total absence of marine fossils, has generally been considered non-marine. That this is at least in part not the case is shown by the presence of limonitized outlines of marine pelecypod casts in exposures back of the beach at the foot of Torrey Pines Grade. Also, a marine shale stratum in the middle of the Torrey sand has been exposed by recent excavating along the new Torrey Pines Grade. It is probable that the Torrey sand indicates a succession of geomorphic events in the crystalline area to the east somewhat similar to that indicated by the quartz sand zone of the Ione formation in the foothills of the Sierra Nevada in eastern central California. In the latter case an uplift of the peneplained Sierras was responsible for the deposition in the coastal lowlands of glass sand, coal and pottery clay with anauxite between Capay and Domengine times. This was pointed out in a paper presented by Mr. F. B. Tolman.'® From Mr. Tolman’s interpretations it follows that the Delmar may correspond in age to some part of the Capay formation and the Torrey sand to Ione or early Domengine time.
In much of the La Jolla Quadrangle the Rose Canyon shale lies conformably on the Torrey sand. Where the Torrey sand is absent the Rose Canyon rests unconformably on the Black Mountain volcanics or on the Cretaceous. Southward the Rose Canyon shale also appears to overlap the Torrey sand. While there is an undoubted unconformity between the La Jolla formation and the Cretaceous, the evidence seems to be indirect except where the Rose Canyon shale member rests nonconformably on the Cretaceous.
The Rose Canyon shale occurs under much of the Kearny or Linda Vista Mesa and also farther south where it underlies the San Diego Pliocene along the south side of Mission Valley. Most of the peninsula of Point Loma consists of Eocene overlying the Cretaceous, but the beds are not very fossiliferous in that area. A few fossils have been collected at the northeastern end of the peninsula,
141 Hanna, M. A., Univ. Calif. Publ. Bull., Dept. Geol. Sci., Vol. 16, no. 8, p. 257, 1927.
142 Holder, C. F., “Pyramids of Del Mar—Erosion of the Pacific Coast,’ Sci. American, Vol. 85, p. 8, 3 figs., 1901. [Discusses badland effect of erosion at several localities along the Pacific coast}.
143 Amer. Assoc. Petrol. Geol., 22nd Ann. Meeting, Los Angeles, Calif., March 17-19, 1937. Program, pp. 61-62.
42 San Dieco Society oF Natura History [Memotrs
which suggests the presence there of the Rose Canyon member of the La Jolla formation. As mentioned later in this paper the Rose Canyon fauna has been recognized in well samples from the region south of San Diego Bay, suggesting that the Rose Canyon shale may be widespread underlying the San Diego formation.
For a more complete list of the species occurring in the Rose Canyon shale the reader is referred to the paleontologic report of Marcus Hanna already mentioned. The following is a very abbreviated list of species reported by Hanna or discovered later by Tolman in the Rose Canyon member of the La Jolla Quadrangle: Acila decisa Conrad, “Crassatellites” semidentata Cooper, Glycymeris rosecan- yonensis M. Hanna, Macoma rosea M. Hanna, Nuculana parkei Anderson and Hanna, Calyptraea diegoana Conrad, Ectinochilus problematica M. Hanna, Ectinochilus canalifer supraplicatus Gabb, Pelecyora aequilateralis Gabb, “Surcula’” lindavistaensis M. Hanna, “Surcula” praeattenuata Gabb, Turritella applini M. Hanna, Turritella scrippsensis M. Hanna, Turritella soledadensis M. Hanna, Aturia myrli M. Hanna, Eutrephoceras hannai Vokes, “Flabellum” sandiegoensis M. Hanna. In addition to these megafossils Mr. F. B. Tolman has collected Discocyclina cloptoni Vaughan, and Dr. H. G. Schenck has reported Discocyclina clarki Cushman in the Rose Canyon shale.'**
The Poway conglomerate, which overlies the La Jolla formation, consists chiefly of conglomerates with occasional lenses of cross-bedded sand. Gray shale lenses containing fossils occur in the lower three hundred feet and considerable soft white chalky caliche is present in the upper part. According to Hanna the Poway is in places conformable with the Rose Canyon shale but in other places an erosional unconformity can be seen. Eastward it rests with marked unconformity on the Black Mountain volcanics. Well records indicate that the Poway reaches a thickness of at least 875 feet.
A few fossils have been found in interbedded marine sediments in the Poway conglomerate. Marcus Hanna reported the following species: Acila lajollaensis M. A. Hanna, Brachidontes ornatus Gabb, Crassatellites mulates M. A. Hanna, Nuculana parkei Anderson and Hanna, Pholadomya murrayensis M. A. Hanna, Pteria cf. pellucida Gabb, Tellina tehachapi Anderson and Hanna, Calyp- traea excentrica Gabb, Discohelix murrayensis M. A. Hanna, Ficopsis remondii Gabb, Ficus mammillatus Gabb, Turritella applini M. A. Hanna, Pseudoliva volutaeformis Gabb. In addition to those given by M. A. Hanna, Dusenbury’” has cited the following six species from the Poway: Cardium brewerii Gabb, Ostrea idriaensis Gabb, Pitar uvasanus Conrad, Solen novacularis Anderson and Hanna, Conus remondii Gabb, Ectinochilus canalifer Gabb. Dusenbury (p. 91), also gave a short list of foraminifera obtained from these beds.
Many years ago Fairbanks called what is now considered a part of the Poway conglomerate an ancient river gravel and traced high elevation gravels which he believed were extensions of it far to the east in the mountains of San Diego County. Much later Ellis and Lee included the Poway in the lower part of the San Diego formation. Hanna, however, found diagnostic Eocene fossils in shaly parts of the Poway, and during the winter of 1931 Mr. L. M. Huey of the staff of the San Diego Society of Natural History collected a small fauna from a freshly opened cut of the Fenton Materials Company’s quarry in Murray Canyon on the north side of Mission Valley. Huey’s locality, which has been visited by many collectors since, is near one of Marcus Hanna’s original localities and in about the same part of the section stratigraphically. The Eocene age of at least the lower part of the Poway is now well established.
Within the last few years a number of specimens of fossil vertebrates have been collected from the Poway conglomerate north of La Mesa. These appear to indicate an upper Eocene age for this part of the Poway. Professor Chester Stock of the California Institute of Technology has studied these specimens and has prepared for us the following statement in regard to them:
“The small collection of specimens obtained by the San Diego Society of Natural History in an excavation for a cesspool north of La Mesa included several jaws and teeth of mammals definitely older than those known from the Tertiary of California. Among the forms recognized are a carnivore, presumably a creodont, an agrio-
144 Another orbitoidal foraminifer resembling (if not identical with) Discocyclina psila Woodring occurs in the Rose Canyon shale above D. clarki and ranges up into the D. cloptoni zone.
145 Dusenbury, Jr., A. N., “A Faunule from the Poway Conglomerate, upper Middle Eocene of San Diego County California,” Micropaleontology Bull., Vol. 3, no. 3, pp. 84-95, 2 figs. [No. 2 unnumbered], June 15, 1932. (Published by advanced students of Micropaleontology at Stanford University, Calif. Printed by Edwards Bros., Inc., Ann Arbor, Michigan).
VotumE II] Marine PLIOCENE OF SAN DIEGO, CALIFORNIA 43
choerid, and a tiny insectivore. Unfortunately the carnivore specimen is too imperfectly preserved to permit definite identification as to genus and species. The agriochoerid and the insectivore resemble comparable types in the Sespe upper Eocene of Ventura County. Since this collection was made, a few additional specimens have been obtained from the Poway in the vicinity of San Diego, the most important of which is a titanothere. The latter, determined on the basis of a skull fragment with teeth, is tentatively referred to the upper Eocene genus Metarhinus. A survey of the fossil mammals from the Poway suggests an upper Eocene age and a faunal stage earlier in time than that recorded from the upper Eocene of the Sespe.”
Much of the Poway contains no fossils and appears to be of continental rather than marine origin and in this respect recalls the Sespe formation of the Ventura basin and other regions to the north.
The Ballena placer workings'*® for the recovery of gold east of Ramona in parts of sections 17, 18, 19, 20 and 21 of T. 13 S., R. 2 E.,, S. B. B. and M., are operated in gravels referred to the Poway conglomerate by Donnelly.'*7 Although Donnelly stated that these gravels were marine, we agree with Fairbanks’ conclusion that they represent a fluviatile deposit.
Although the Eocene is not known in surface exposures in the San Diego Quadrangle south and southeast of Balboa Park, some of the wells drilled in the south bay region have penetrated Eocene strata. Through the kind cooperation of Mr. J. E. Pettijohn, we have had access to the geological reports of George H. Doane on the San Diego Gas and Petroleum Corporation’s Holderness No. 1 Well in the southeast quarter of section 32, Township 18 S., Range 2 West, San Bernardino Base and Meridian, near the mouth of the Tia Juana River. This well penetrated over a thousand feet of Eocene shales, sandstones and conglomerates, some of which contained diagnostic Eocene fossils.'** According to Mr. Doane, Discocyclina clarki Cushman was found in the cores from 2,946-2,959 feet and 3,286-3,289 feet. In cores from 3,195-3,289 feet Eosolen novacularis Anderson and Hanna was obtained and Cyclinella bunkeri M. Hanna occurred between 3,286 and 3,289 feet. Between 3,289 and 3,324 feet the following were identified: “Flabellum” sandiegoensis M. Hanna, “Tellina”’ cf. scrippsensis M. Hanna (young), “Cardium” sorrentoensis M. Hanna, Corbula cliffensis M. Hanna, Turritella applini M. Hanna, Acila decisa Conrad and “Cardita” sandiegoensis M. Hanna. These fossils indicate the presence of the Rose Canyon member of the La Jolla formation. In three horizons between 4,498 and 4,795 feet Baculites chicoensis Trask was identified. This species is characteristic of the Cretaceous. Dr. G. D. Hanna and C. C. Church have furnished us a report on a core of this well from a depth of 3,706 feet as follows: “Gray, sandy, micaceous shale with abundant carbonized plant remains, shell impressions and foraminifera: Cibicides sp., Eponides mexicana Cushman, Robulus inornatus d’Orbigny, Robulus mexicanus var. nudicostatus Cushman & Hanna, Siphonina cf. jackson- ensis Cushman & Applin. Eocene. Domengine.” It is likely that the Eocene is widespread below the San Diego formation in the region south of the San Diego River Valley but is overlapped by the Pliocene eastward.
From time to time attempts have been made to obtain coal in the San Diego region. It is now impossible to locate accurately these reported carbonaceous deposits, but some of the coal beds have been reported in localities where Eocene strata are exposed at the surface. Tyson,’ in 1850, stated: “Tt had been reiterated over and over again in letters, newspapers, and in other ways, that there was, a few miles north of this port, near the seashore, a coal formation capable of furnishing ample supplies of the ‘best of coal for steamers’ and other purposes. These beds prove to be layers of bitumen an inch or two thick, alternating with thin strata of small gravel and sand.” Many years ago the San Diego Herald,!” published in San Diego, stated (1856) that coal was found on Lewis Rose’s ranch
about five miles from town. According to this paper, prospectors on Rose’s ranch dug to a depth of
146 Fairbanks, H. W., Calif. State Mining Bureau, 11th Ann. Rept. State Mineralogist, Vol. 11, p. 91, 1893. — Merrill, F. J. H., Calif. State Min. Bureau, 14th Ann. Rept. State Mineralogist, p. 652, 1916. Issued as a separate Dec., 1914.
147 Donnelly, M., Calif. Journ. Mines and Geol., Calif. State Mining Bureau, 30th Rept. State Mineralogist, Vol. 30, no. 4, p. 369, Oct., 1934.
148 The column, as constructed by George H. Doane from a study of the cores and ditch samples, is included in the present report under the treatment of the San Diego formation.
149 Tyson, P. T., “Geology and Industrial Resources of California,” Senate Ex. Doc. 47, 31st Congress, Ist Session, 1850 (reprinted with an introduction, published by Wm. Minifie and Co., Baltimore, 1851), p. 20.
150 The San Diego Herald, Vol. 6, June 28, 1856, p. 2, col. 1.
44 San Dreco Society oF Naturat History {[Memotrs
120 feet. Later The Daily World,'’’ also published at San Diego, contained a notice (1872) of a meeting of the owners of the “Soledad Coal Mines.” These mines are said to have been located in Rose Canyon. The type locality of the Rose Canyon shale of Eocene age is at the bend of Rose Canyon. Old records indicate that a coal mine once existed a few miles farther north somewhere near the present location of the town of Del Mar. This is shown on a manuscript map'” drawn in 1850 by Lieutenant Cave Johnson Couts of the First Dragoons, U. S. Army.
The lignitic Delmar member of the La Jolla formation exposed at the base of the beach bluff at Torrey Pines on the south side of the mouth of Soledad Canyon was briefly described in 1857 by William H. Emory, then Major, First Cavalry, and United States Boundary Commissioner.'”? Probably the Del Mar coal mine was an attempt to obtain coal of commercial value from this Delmar member of the La Jolla formation although we did not attempt to locate the exact position of this mine.'”* Merrill’”’ discussed the occurrence of coal near Del Mar in his report on the mineral resources of San Diego County. Eocene rocks are exposed in this area, as shown on the map by Marcus Hanna. The coal reported in a boring at La Jolla occurred in Cretaceous rocks, according to Fairbanks.'*°
Inasmuch as some of the Eocene sandstones are similar in general field appearance to some facies of the Pliocene sands, we include here a sedimentary analysis of an Eocene sample for comparison.
This analysis has been made for us by Dr. Gordon A. Macdonald.
No. 14. Eocene lithologic sample: north side of gully just north of Mercy Hospital on 6th Avenue Grade to Mission Valley. Ten feet below conglomerate. L. G. Hertlein and U. S. Grant, rv, collectors. August 12, 1937.
LIGHT MINERALS:
(ORT of ee arr reser try Seba eet a ern eee 54.9% Orthoclase ............--.-. Forth ee aN Sn aR EEE 25.0% Oligoclases zi ee S ae Pen acttsccctesinesetw lan 15.0% Al Bite ee ite ore ee See SE a A 4.0% FETFIA VY gu ROADS ne eotere tee ere ce rg eee shee aon occa Ss IGG
Magnetite—very rare Ilmenite—moderately abundant Epidote—abundant Zoisite—abundant
Pink garnet—rather rare Titanite—rather rare Andalusite—rare
Zircon—rare Piedmontite—rather rare
“The grains vary from .05 to ca. .4 mm. in diameter, and average ca. .2 mm. They are largely angular, but some are subangular. The sorting is rather good. The orthoclase feldspar is considerably kaolinized. “This Eocene sample is very unusual, in that the heavy fraction is made up very largely of epidote and
151The Daily World, Vol. 1, no. 73, Oct. 16, 1872 [on unnumbered p. 3]. This reference was called to our attention by Mr. John Davidson, Curator of the Junipero Serra Museum of the San Diego Historical Society.
152 This map was shown to us by Mr. Cave J. Couts of the Guajome Rancho, near Oceanside, San Diego County, son of the author of the map. A reproduction of this map was included by Fr. Zephyrin Engelhardt in his work “The Missions and Missionaries of California,’ New Series, Local history, San Luis Rey Mission, (San Francisco, California, 1921), p. 257.
153 Rept. United States and Mexican Boundary Surv., Vol. 1, pt. 2, p. 90, and text figure on p. 85, 1857. Emory stated that the lignite was not of economic importance.
154 Most if not all of the reports of the occurrence of “coal” in the San Diego region are based upon the existence of bituminous beds in the Eocene or the Cretaceous. Many years ago Goodyear reported “‘coal’ ’and “slate rock with some coal” at, respectively, 177 feet and 245 feet depths in a well which had been sunk for the purpose of securing artesian water “‘on the east side of the bay, at a point where the mouth of the well was ninety-four and one-half feet above high water.” From the text Goodyear appears to refer to San Diego Bay. If this is correct the well must have been in the Pliocene or in a deposit of later age. If he had been referring to Mission Bay instead of San Diego Bay the well could have been in the Eocene. See Goodyear, W. A., Calif. State Mining Bureau, 8th Ann. Rept. State Mineralogist, p. 518, 1888.
155 Merrill, F. J. H., Calif. State Mining Bureau, 14th Rept. State Mineralogist, p. 713, July, 1915 (1916). Also issued as a separate, “Geology and Mineral Resources of San Diego and Imperial Counties,” Dec., 1914, p. 83. “Lignite seams of limited thickness and extent have been reported from borings in the vicinity of San Diego, and tradition says that some thirty years ago a bed of coal exposed at low-water mark, in the beach near Del Mar, was worked as a source of fuel for blacksmith forges.”
156 Fairbanks, H. W., Calif. Stare Mining Bureau, 11th Ann. Rept. State Mineralogist, Vol. 11, p. 96, 1893.
VotumE II) MarINE PLIOCENE OF SAN DIEGO, CALIFORNIA 45
zoisite, with a little of the rare mineral piedmontite. The fact that the only minerals left in the heavy fraction are of types which are resistant to chemical decomposition suggests that the Eocene may have been a time of pronounced chemical weathering. This of course corresponds well with the known character of the Ione and Capay sands. However, it is risky to attempt any conclusions on the basis of a single sample. The fact that the feldspar is still recognizable in this sample, although somewhat kaolinized, suggests that conditions were less severe than in the case of the Ione, or, which would bring about the same result, that erosion was more rapid in the San Diego region than in the source areas of the Ione.” (G. A. Macdonald).
At several localities in the coastal region between Rose Canyon and Carlsbad, Eocene shales and clays are of suitable quality for the manufacture of brick, tile and pottery. For many years brick has been manufactured in Rose Canyon. At the present time the Union Brick Company operates on about 100 acres in this canyon. The Vitrified Products Corporation of Old Town controls clay properties five miles northeast of Cardiff and also two miles north of Linda Vista. The Pacific Clay Products Company of Los Angeles controls about thirty-five acres on the Agua Hedionda Land Grant near Carlsbad. All of these properties are benefited by good transportation facilities afforded by the Santa Fe Railroad and the paved highways.
ABSENCE OF OLIGOCENE AND MIOCENE ROCKS IN THE SAN DIEGO REGION
Oligocene sediments are absent in the San Diego region so far as now known. There are no sediments present between the Eocene and Pliocene at any of the known localities in that area and no Oligocene fauna has been reported in the extreme southern part of the State.
Miocene sediments are likewise absent in the area under discussion. In 1909 Tempére and Pera- gallo!” listed 75 species of diatoms from “San Diego-Californie (Etats-Unis) Dépét fossile marin.” A careful examination of this list shows that the material undoubtedly came from some California locality of upper Miocene (Monterey) age. It was probably transmitted to Paris by some microscopist to whom the beauty of the fossils was appealing and the need of exact locality data was not apparent. The material may have come from any one of a great many known exposures, but probably was obtained somewhere in the vicinity of Capistrano where beds of the same age do outcrop. Many years ago C. R. Orcutt'”® reported “a specimen of diatomaceous earth from the ocean beach near San Diego.” It was stated that this specimen was “very like some samples of the Redondo Beach deposit, and may have been washed from there.” Orcutt’s specimen undoubtedly came from a source nearer than Redondo, perhaps from the vicinity of Capistrano. North of Capistrano, beds of Vaqueros age con- taining the Turritella inezana fauna have been reported by Woodford.’ Beds of Temblor age also occur in the north but they are likewise lacking in the area under discussion.
Blake and Conrad appear to be responsible for an early report of the presence of Miocene strata in the San Diego region. In Volume 5 of the U. S. Pacific Railway Reports, Blake stated:'®° “Before leaving the Mission of San Diego, a block of sandstone, filled with fossils, was handed to me, but the locality was not seen. It is a compact sandstone, not unlike that of the Bay of San Francisco and Oregon. Mr. Conrad finds it to contain the following species: Cardium modestum, Nucula decisa, Corbula Diegoana, Mactra Diegoana, Natica Diegoana, Trochita Diegoana, Tellina Diegoana, and T. congesta. He also remarks a palaeontological relation between these fossils and those of Monterey, Carmello, and those found in boulders in Oregon by Mr. Townsend and Professor Dana.” These species were described by Conrad in an Appendix of the same volume’®' under the heading: “Fossils
157 Tempére, J., and Peragallo, H., “Diatomées du Monde Entier,” Ed. 2, pp. 160-161, 1907-1915. [These pages issued in 1909]. See also edition 1 (Paris), 1889-1895, pp. 271-272. Dr. G. D. Hanna kindly called these references to the attention of the authors. See Hanna, G. D., Bull. de la Soc. Franc. de Microscopie, Vol. 5, no. 3, p. 110, 1936.
158 Orcutt, C. R., West Amer. Sci., Vol. 7, whole no. 57, p. 136, Feb., 1891. 159 Woodford, A. O., Univ. Calif. Publ. Bull. Dept. Geol. Sci., Vol. 15, no. 7, pp. 178-180, 1925.
160 Blake, W. P., U. S. Senate Ex. Doc. 78, and House of Representatives, Ex. Doc. 91, 33rd Congress, 2nd Session, “Reports of Explorations and Surveys to Ascertain the Most Practicable and Economical Route for a Railroad from the Mississippi River to the Pacific Ocean,” etc., Vol. 5, pt. 2, Geological Rept., chap. 13, p. 176, 1857.
161 See pages 322-327. These species were actually first described without figures in House Doc. 129, Projected Vol. 3, 33rd Congress, Ist Session, 1855, Ap. to Report of W. P. Blake, pp. 11-18.
46 San Disco Society oF Naturat History [Memorrs
of the Miocene and Recent Formations of California.” These species are now known to be Eocene fossils with the exception of “Tellina” congesta, the type of which is said to have come from the Miocene Monterey shale near Monterey, California.'®
Ellis? mentioned some fossils collected in south Las Choyas Valley which Dall determined as “upper Miocene or probably Pliocene.” Other fossils collected about 31/, miles east of Chula Vista in a canyon locally known as Fossil Canyon, were determined by Dall to be of upper Miocene age, according to Ellis (p. 63). This latter locality is a well known Pliocene fossil bed from which the present authors have collected a small but distinctly Pliocene fauna.
Merrill'®* in 1914 pointed out that beds of middle Miocene age, which are the chief source rocks of oil in the San Joaquin Valley and Orange County, California, are lacking in San Diego County and that the deepest wells drilled have passed through the Tertiary and Cretaceous strata and penetrated a black shale, sometimes calcareous, which he suggested was probably of Jurassic age, although no faunal evidence for that age is known. Asphalt reported along the coast was considered to have come from long distances and not from the region about San Diego. Merrill’s report indicated that there is but little chance for petroleum to be found in San Diego County and pointed out that drilling, while laudable as evincing a cordial public spirit, should only be undertaken by people or companies able to stand a loss, due to the fact that the possibility of finding oil in commercial quantities is slight. The present authors are inclined to agree with Merrill’s conclusion.
The logs of a number of wells which have been dug or drilled in the San Diego region have been given by Ellis'®’ in his report on the water resources of western San Diego County, and by the present authors in a recent paper.’*° Some of these well logs are mentioned briefly in the present paper in the discussion of the Cretaceous and of the Pliocene.
PLIOCENE In 1874 W. H. Dall’® listed and discussed the fossil mollusks collected by Henry Hemphill
from the material removed in digging a well for water in San Diego. The well was located near the mouth of what is now known as Cabrillo Canyon in Balboa Park. Although this well has long since been filled in, the brick lining of the mouth of the well can still be seen at the date of this writing (October, 1939) in a grassy swale near two eucalyptus trees. It is located “on the northerly prolongation of the east line of Eleventh Avenue, 85 feet north from the easterly production of the north line of Beech Street.”’®* The elevation of the ground at the well-head is approximately 96 feet above mean sea level and as the well was stated to have attained a depth of 160 feet, the bottom was considerably below sea level. The mouth of the well is brick-lined and has a diameter of about 102 feet. The location of the well is shown on the contour map (text figure la) and the sequence of some of the fossil beds penetrated by the well are shown in the accompanying cross section (text figure 1b). Although the strata encountered in the well were said to be fossiliferous throughout, the lower beds, from which Dall stated most of his specimens came, were not discovered by us outcropping in the immediate environs of the well. The large scale one-foot contour interval map of Balboa Park in the City Engineer’s Office and a recent Transit survey determine the dip of the beds in the vicinity of the well to be 4°, in a direction south 33° 30’ west. If the dip and strike of the beds remain constant, the fossiliferous strata at the bottom of the well might be expected to outcrop in the bottom of Cabrillo Canyon between Juniper and Laurel Streets projected.
Dall concluded that the age of the fossils obtained from the well was Pliocene. This was the
162 Schuchert, Charles, assisted by Dall, W. H., Stanton, T. W., and Bassler, R. S., U. S. Nat. Mus., Bull. 53, Pr. 1, p. 643, 1905. According to Dall (U. S. Geol. Surv., Prof. Paper 59, p. 126, 1909) this species appears to be a Macoma. The San Diego Eocene species to which the name congesta was erroneously applied by Conrad, is not known to the present authors.
163 Ellis, A. J., in Ellis, A. J., and Lee, C. H., U. S. Geol. Surv., Water Supply Paper 446, p. 62, 1919.
164 Merrill, F. J. H., Calif. State Mining Bureau, Bull. 69, pp. 467-468, 1916. Issued as a separate Dec., 1914.
165 Ellis, A. J., in Ellis, A. J., and Lee, C. H., U. S. Geol. Surv. Water Supply Paper 446, pp. 55-68, 1919.
166 Hertlein, L. G., and Grant, 1v, U. S., Calif. Journ. Mines and Geol., Vol. 35, no. 1, 35th Rept. Calif. State Mineralogist, pp. 74-77, Jan., 1939, [received at library of the California Academy of Sciences Aug. 23, 1939).
167 Dall, W. H., Proc. Calif. Acad. Sci., Vol. 5, pp. 296-299, 1874.
168 Data from H. W. Jorgensen, City Engineer of San Diego, letter of April 7, 1939.
47
MarINE PLIOCENE OF SAN D1kGO, CALIFORNIA
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48
San Dieco Society oF Naturat History [Memoirs
first faunal assemblage of any size in California to be definitely placed in the Pliocene, and hence that locality is one of the early well-defined Pliocene localities of the State. As Dall’s early paper is now becoming quite rare, we reproduce below the list of fossils exactly as given by Dall together with what we consider are the proper names of the species represented, in modern nomenclature, in the column at the right.
P. 296 ao! ped os “ 4. 5, “6
“Ee
Exact Copy or OriGinat List
Glottidia albida, Dall ex Hinds.” Xylotrya, sp. indet. Tube only.” Cryptomya Californica, Contr.” Solen rosaceus, Cpr.”
Solecurtus Californianus, Conr.” Macoma (var.?) expansa, Cpr.”
. Callista, sp. indet. Smooth, inflated, thin; much
like Callista Newcombiana, erroneously de-
scribed as Lioconcha by Gabb.”
. Cardium centifilosum, Cpr.” . Venericardia borealis, Conr.” . Lucina nuttallii, Conr.”
. Lucina borealis, Linn.”
. Lucina tenuisculpta, Cpr.”
. Cryptodon flexuosus, Mont.” . Modiola recta, Conr.”
. Arca microdonta, Conr.”
. Nucula, sp. n. according to Dr. Cooper; named
in MSS. by Carpenter. Looks much like N.
tenuis.”
. Acila Lyallii, Baird. This species has been fre-
quently reported as castrensis, Hds.”
. Leda coelata, Hinds.”
. Pecten hastatus, Sby.”
. Amusium caurinum, Gld.”
. Janira florida, Hds.”
. Ostrea conchaphila, Cpr.”
. Placunanomia macroschisma, Desh.”
. Tornatina eximia, Baird.”
. Cylichna cylindracea, Linn.”
. Dentalium hexagonum, Sby.”
. Dentalium semipolitum, B. and S.”
. Siphonodentalium pusillum(?), Gabb.” . Calliostoma annulatum, Mart.”
. Galerus filosus, Gabb, as Trochita.”
. Crepidula navicelloides, Nutt.”
. Crepidula princeps, Conr. This is not grandis
of Midd.”
. Turritella Jewettii, Cpr.” . Bittium asperum, Cpr.”
Myurella simplex, Cpr.”
“36-39. Drillia, sp. indet. This and three other
“41.
forms of Drillia so closely resemble Gulf forms, that it is inadvisable to describe them without a comparison of specimens.”
Surcula Carpenteriana, Gabb, and variety Try- oniana, can hardly be separated as species. The transition is very gradual and complete.” Mangelia variegata, Cpr.”
“42-45. Mangelia, spp. indet. The same remark ap-
plies here as to No. 36.”
PROBABLE EQUIVALENT IN MODERN NoMENCLATURE
Glottidia albida Hinds
Xylotrya sp.
Cryptomya californica Conrad
Solen rosaceus Carpenter
Tagelus californianus Conrad
Tellina expansa Carpenter or Tellina (Oudaria) buttoni Dall
?Compsomyax subdiaphana Carpenter
Nemocardium centifilosum Carpenter Cardita (Cyclocardia) ventricosa Gould Lucina (Lucinisca) nuttalli Conrad
Lucina (Lucinoma) annulata Reeve Lucina (Parvilucina) tenuisculpta Carpenter Thyasira gouldii Philippi
Volsella { = Modiolus} recta Conrad
Arca trilineata Conrad
Nucula exigua Sowerby
Acila castrensis Hinds
Nuculana taphria Dall
Pecten (Chlamys) hastatus Sowerby
Pecten (Patinopecten) healeyi Arnold Pecten (Pecten) stearnsti Dall
Ostrea conchaphila Carpenter
Pododesmus macrochismus Deshayes Acteocina eximia Baird
Cylichnella alba Brown
Dentalium neohexagonum Sharp and Pilsbry Dentalium semipolitum Broderip and Sowerby Cadulus fusiformis Pilsbry and Sharp Calliostoma annulatum M
Calyptraea (Trochita) filosa Gabb Crepidula nummaria Gould
Crepidula princeps Conrad
Turritella jewettii Carpenter
Bittium (Lirobittium) asperum Gabb Terebra martini English
? Possibly Clathrodrillia, four new species
Megasurcula carpenteriana Gabb
Mangelia barbarensis I. S. Oldroyd ? Possibly Mangelia n. sp., and others
VoLuME II]
Exact Copy or Oricinat List
“46. Clathurella Conradiana, Gabb. The specimens are slightly stouter than Gabb’s figure, but vary among themselves in this respect, and in other characters are similar to his species.”
“47. Odostomia straminea, Cpr. var.”
“48. Odostomia, sp. indet. Very imperfect.”
“49. Chemnitzia torquata, Cpr.”
“50. Eulima rutila, Cpr.”
“51. Scalaria subcoronata, Cpr.”
“52-55. Cancellaria, 4 spp. indet. Most of them, as far as memory serves, resemble southern forms not at hand for comparison.”
“56. Neverita Recluziana, Petit.”
P. 298
“57. Sigaretus debilis, Gld.” “58. Ranella Mathewsonii, Gabb.”
MarINE PLIOCENE OF SAN D1EGO, CALIFORNIA 49
PRoBaBLE EQUIVALENT IN MopERN NoMENCLATURB
Glyphostoma conradiana Gabb
?Odostomia (Evalea) tenuisculpta Carpenter
Odostomia sp.
?Turbonilla (Strioturbonilla) torquata Carpenter
Melanella (Eulima) rutila Carpenter or Strombiformis riversi Bartsch
Probably Epitonium (Nitidiscala) tinctum Carpenter
Probably Cancellaria arnoldi Dall, C. hemphilli Dall, C. crawfordiana Dall, and Cancellaria, n. sp.
Polinices (Neverita) reclusianus Deshayes
Sinum debile Gould
Gyrineum lewisii Carson
“59. Olivella boetica, Cpr.”
“60. Nassa fossata, Gld.”
“61. Nassa mendica, Gld.”
“62. Astyris tuberosa, Cpr.”
“63. Astyris, sp. indet. jun.”
“64. Ocinebra lurida, Cpr.”
“65. Pteronotus festivus, Hinds.”
“66. Trophon orpheus, Gld.”
“67. Fusus (Colus) Dupetit-Thouarsi ? Kien.”
“68. Chrysodomus, n. s. Too imperfect for descrip- tion, but very distinct; perhaps a Volutopsis, as the nucleus would indicate.”
“69. Chrysodomus Diegoénsis, n. s.”
Olivella pedroana Conrad
Nassarius (Schizopyga) fossatus Gould Nassarius (Schizopyga) mendicus Gould Mitrella tuberosa Carpenter
Mitrella sp. or Cosmioconcha n. sp. Ocenebra lurida Middendorff
Triremis festiva Hinds
Trophon (Boreotrophon) stuarti E. A. Smith
Fusinus (Barbarofusus) ?barbarensis Trask
Searlesia diegoénsis Dall
Dall'® later referred to the sediments from which the San Diego well fossils were obtained as the “San Diego Beds” and Arnold'”® referred to these fossiliferous sands as the “San Diego formation.” Although Arnold'’! described in much greater detail the Pliocene sandstones of Pacific Beach and listed a considerable fauna from them, the San Diego well must be considered the type locality of the San Diego formation. This is unfortunate, since the historic well has long since been filled in and an outcrop of beds with an identical fauna has not yet been definitely located in the immediate environs. Due to the fact that the San Diego formation cannot readily be divided into members which can be recognized at different localities, it is entirely reasonable to include in the San Diego formation all the marine Pliocene sedimentary beds of the region, with the exception of the overlying reddish-brown conglomeratic sandstone which caps most of the mesas and which may be of late Pliocene or Pleistocene age.
The Pliocene exposed in the beach bluffs at Pacific Beach, however, may represent a higher part of the Pliocene than the Trophosycon beds exposed in the road cut below the Mercy Hospital and the Pliocene fine sands exposed along India Street. The Pacific Beach beds are not continuous in surface exposures with the Pliocene in the San Diego Mesa and with just what part of the latter the Pacific Beach beds correlate cannot be stated definitely now. Some of the older forms found in the mesa Pliocene, such as Trophosycon, have not yet been discovered at Pacific Beach.
DISTRIBUTION
Pliocene beds here referred to the San Diego formation compose the greater part of the mesa-
169 Dall, W. H., U. S. Geol. Surv., 18th Ann. Rept., Pt. 2, 1898, opp. p. 334, p. 337. 170 Arnold, R., Journ. Geol., Vol. 10, p. 130, 1902. According to Arnold the San Diego well was 149 feet deep. 71 Arnold, R., Mem. Calif. Acad. Sci., Vol. 3, pp. 57-58, 1903. — U. S. Geol. Surv., Prof. Paper 47, p. 28, 1906.
50 San Dreco Society oF Naturat History [Memors
lands of the San Diego region, and cover a large area from the south slope of the San Diego River Valley to some distance beyond the Mexican Boundary. They also outcrop on the lower southern slopes of Mount Soledad and in the bluff behind the beach at Pacific Beach. No Pliocene is known to occur in the Linda Vista Mesa north of the San Diego River Valley nor on Point Loma.
The contact between the known Pliocene sediments and the Eocene and older rocks is indicated on the map (text figure 2). Over much of the region the Pliocene sandstones are covered by a mantle
Section AAU Pawt
> Baacs\|
Yoo, TI6S. Y V4}
Or MOUNT HELIX ta} LG tty py
VAL
SXANN
Se Cretaceous over/ain by \ Eocene with marrow .
Pleistocene terrace \We \ along shore \ a) y+ PT. poe Hs
Cretaceous exposed along shore
NNNAS
LEGEND
—___ Detinite Fault — ~~ Probable Fau/t on" Aypothetical Fault
Quaternary marine and non-marine tara S x27 At n S Z 4 ities race deposits, valley Fill, efc. WHE SSS . L, Nx
FRAY “erine San Diege Pliocene. Generally : QI WAeescan NSS)
overlain by Sweitzer conglomerate Soult \ we of Sun Diego River valley }
(TEA) Marine Eocene including Poway conglem- | i} COTAY MESA |
erate
t Pre-Tartiary igneous and metamor- i Ste Aten rocks prasimcaty Mesoxole “me? Serer SS SSAA Sb . See c + —- —- — Boundary of Tawnship \ pokey Ds FAGALIESE RIE —: —: — Boundary of Land Grant. R Ss = P= M SCALE lho 1 2 3 4 S Miles | ess es ees |
Geology ty £6 Hertlain and US Grant, @ Base from San Diego County Map.
Text Fic. 2. Map of areal geology of the San Diego region, Quaternary sediments on the mesas and on some of the higher terraces have been omitted. To have included them all would obscure the true distribution of the older deposits. The small scale of this map has made it impracticable to attempt to delineate the distribution of the upper Cretaceous rocks exposed in the sea-cliffs along the southern half of Point Loma. Due to the scale, certain narrow Pleistocene terrace deposits which occur along the west shore of Point Loma have also been omitted. The intermittent streams have been emphasized to bring out the drainage direction and pattern. The mine symbol on the west side of Point Loma indicates the position of the “Coal Mine” which is about 134 miles north of the lighthouse at the end of Point Loma. The topo- graphy of this region is shown on U. S, Geological Survey Maps of the San Diego, La Jolla, Cuyamaca, and E] Cajon quadrangles.
of later terrace material and soil which has not been indicated on the map. A great part of the mesa south of the San Diego River Valley is capped by a characteristic reddish-brown conglomerate, which has been named the Sweitzer formation. Due to the limited time which could be devoted to field work and the small scale of the map, it has not been possible to plot the contact between the San Diego formation and the overlying Sweitzer formation. All of the Coronado peninsula, including North Island, the terrace upon which the business section of the City of San Diego has been built, the Pacific Beach-Crown Point Terrace, and the lower terraces east of the southern part of the San Diego Bay are of Pleistocene age as shown by numerous deposits of Pleistocene fossils.
VotumE II} Marine PLIOCENE OF SAN D1kGO, CALIFORNIA 51 LITHOLOGY AND SEDIMENTATION
Lithologically the San Diego formation consists of generally fine-grained sands of a bluish-grey to yellowish-brown color, with occasional layers and lenses of gravel. Where the sand is very fine-grained and of a light bluish-gray color, it is difficult to distinguish from some of the Eocene sandstones exposed just to the north of the Pliocene basin. Fine-grained sands, often micaceous, compose the bulk of the observed thickness of the San Diego formation, but locally it grades into coarser sand and occasionally gravel and lenses or layers of conglomerates. In the mesa on the south side of Tia Juana Valley, about one mile west of the Boundary School, a considerable thickness of conglomerates
EOCENE-PLIOCENE CONTACT PLIOCENE-PLEISTOCENE CONTACT SECTION A-A‘
PLEISTOCENE SANOS
SWEITZER CONGLOMERATE
ke i) SANDSTONE SHOWING
OCCASIONAL INDURATED LAYERS 94 =
Sey N VALLEY ALLUVIUM PLEISTOCENE SEA ae EOCENE SANDY SHALE
SECTION 8-8’
Text Fic, 3. Section A-A’. Generalized section of Pacific Beach Pliocene deposits as exposed in the bluff facing the beach. Total distance north to south about 3,850 feet. Vertical scale greatly exaggerated Pecten healeyi occurs most abundantly in the lower half of the beds exposed in this section. Beds in the upper half of the section contain abundant specimens of Pecten bellus.
Section B-B’. Diagrammatic sketch showing the relationships of the Pliocene San Diego formation to the Eocene, to the Sweitzer formation on Sixth Avenue, and to the Pleistocene. Section approximately north and south from Mission Grade to foot of 26th Street. Distance about 5 miles. Vertical scale greatly exaggerated.
The locations of the cross-sections are shown on the map in text figure 2.
and coarse indurated sands is exposed in a small steep canyon on the United States side of the Mexican Boundary. This conglomerate stratum is fully 100 feet thick, and the larger boulders range up to three feet in maximum diameter. The discovery of a Pliocene fossil locality not far to the west suggests that this conglomerate is also Pliocene in age and the equivalent of the San Diego formation of Otay Mesa and other Pliocene mesas farther north. The boulders are moderately well rounded and consist of hard dense crystalline rocks of varying colors. The source of the boulders may have been some of the nearby mountains just south of the Border in Lower California. Coarse-grained sand- stones are uncommon in general in the San Diego formation but a prominent outcrop of very coarse- grained gravelly sandstone occurs in a spur between the two northeastern extensions of Paradise Valley, about three and a quarter miles west of Sweetwater Reservoir (Plate 10, figure 2).
The other lithologic extreme met with in the San Diego formation is represented by marly material which occurs in pockets or seams, and rarely in beds of nearly pure white marl. Due to the fact that much of the mesa region is mantled by soil which is effectively held in place, even on
52
San Dreco Society oF Naturat History
pecen
BAY POINT FORMATION
QUATERNARY
SWEITZER FORMATION
SAN DIEGO FORMATION
POWAY CONGLOMERATE
TERTIARY
ALLUVIUM Ri
ROSE CANYON SHALE
TORREY SAND
MARINE UPPER CRETACEOUS AT ILA JOLLA, PT. LOMA ANDIN VARIOUS WELLS
NON=MARINE RETACEOUS PENE— TRATED IN WELLS PROBABLY EQUIVALENT TO T TRABUCO FORM. OF THE SANTA ANA MTS.
Ww z Ww .) ° Fe 2 @ w 4 i vo Q WwW a ri ro) o uw ” 3 Ww 18) < ¥ VO
MESOZOIC
TRIASSIC OR JURASSIC
BLACK MOUNTAIN VOLCANICS
0-300’ Beach deposits, valley fill and terrace deposits, gravel, sand and silt
1-30" Marine fossiliferous terrace deposits and non-marine valley fill, gravel, sand and silt
5-30’ Conglomerate and conglomeratic sand- stone, generally brown or reddish brown
1250’ Soft yellowish and gray sands, sometimes micaceous or marly, often fossiliferous, with minor amounts of conglomerate
875° Massive conglomerates with sand or clay matrix With occasional coarse or fine brown sand or gray sandy rarely fossiliferous shale
300’ Blue to gray sandy shale with thin limey fossiliferous beds.
Coarse and fine-grained sandstones grad into penacecde shales with occasional carbon—
1000-2000" Hard well stratified sandstones sometimes concretionary and gray or black shales. Fossiliferous.
250-1000" Hard reddish sandstones and con- glomerates
2000” Basalt flows, agglomerates, sitered shale and sandstone cut by later dikes and intruded by acidic plutonic rock.
Text Fic, 4. Columnar section of the rocks exposed in the southwestern part of San Diego County. This section, except the Cretaceous part, is compiled from observations of surface
exposures of the rocks.
from well logs.
The Cretaceous section is compiled
[Memoirs
VotumE II] MarINE PLIOCENE OF SAN D1EGO, CALIFORNIA 53
the slopes, by brush and lichens, moss and small ferns, no estimate of the Proportion, nor idea of the regularity in distribution of these chalky deposits could be obtained; but they appear to be more common in the eastern parts of the mesas. These marly deposits are exposed at several places in the eastern Otay region and on the edge of the mesa north of the upper reaches of Las Choyas Valley. It is possible that the thicker beds represent quieter and slower deposition on the leeward sides of projecting promontories of pre-Tertiary hard rock, some of which now form foothills in that district. The seams and pockets may be due to a concentration of limy material by percolating waters.
A dark colored bentonite bed eight inches to one foot thick occurs in the Pliocene yellowish-brown and gray sands exposed in a road cut on Federal Avenue about 400 feet east of 35th Street. During the construction of an elevator shaft at the east end of the Natural History Museum Building in Balboa Park in the spring of 1943, a stratum of volcanic ash was encountered which appears to be a water-laid bentonite and is the most northerly known occurrence of volcanic ash in the San Diego Pliocene. A sample was examined from the bottom of the shaft at a depth of 56 feet below the ground floor of the building. This would be at an elevation of approximately 232 feet above mean sea level. The general decrease in dip of the San Diego formation southeasterly from Balboa Park suggests that this bentonite may be at about the same stratigraphic position as the bentonite mentioned above which is exposed on Federal Avenue, several miles southeasterly from Balboa Park. The only other bentonite known to us in the Pliocene of this region is that which occurs on the north and south sides of Otay Valley. These bentonite beds are an exceptional phase of the lithology of the San Diego formation, which is characteristically fine sand.
The sediments of the San Diego formation, taken as a whole, represent deposits which have accumulated in relatively shallow water. The occasional cross-bedding, lenses and layers of conglomer- ate, and the lack of shale, all point to a depth of water from low tide to possibly fifty fathoms. This is borne out to a great extent by the fossils, including the Mollusca, Echini and Foraminifera. In this ecologic aspect the San Diego Pliocene is unlike equivalent horizons in the Los Angeles basin, other than the rare marginal shallow water facies.
Dr. Gordon A. Macdonald has made a petrographic study of samples of Pliocene sediments collected by us at several localities. His report on these sediments is included here.
No. 15. Pliocene. Road-cut S-SE of Mercy Hospital on 6th Avenue Grade to Mission Valley. This is above the Trophosycon beds. L. G. Hertlein and U. S. Grant, rv, collectors. August 12, 1937.
LIGHT MINERALS:
Quartz Seon esate Sse aol teva schy ates ALB Orthoclaseyes tone eee, Fe a .. 29.9% Oligoclases = eee hee coed Mya ere 19.9% Al bite os fe fer ce oe IE csc ie HLS 5.0% HEAVY MINERALS: .........0-2000000000-0+ Pein Sees, LY ETO
Magnetite—rare Ilmenite—moderately abundant Green hornblende—abundant Actinolite—abundant Epidote—moderately abundant Zoisite—moderately abundant Titanite—moderately abundant Zircon—moderately abundant Colorless garnet—moderately abundant Glaucophane—rather rare Brown biotite—rather rare Brown hornblende—rather rare Rutile—rare
“The grains are angular, with a few subangular. They vary from about .01 to .05 mm. in diameter, the average being about .02 mm. The sorting is good. The feldspar is largely unaltered.” (G. A. Macdonald).
No. 16. Pliocene. Southeast corner of India and Upas Streets. One foot below fossil zone. L. G. Hertlein and U. S. Grant, rv, collectors. August 13, 1937.
54 San Dreco Soctety oF Naturat History [Memorrs
LIGHT MINERALS:
Albite
AHAVY: MINERALS * (oUt PN. CeMeME E Ye Magnetite—rare Ilmenite—moderately abundant Green hornblende—abundant Actinolite—moderately abundant Titanite—moderately abundant Zircon—moderately abundant Epidote—rather rare Zoisite—rather rare Brown biotite—rather rare Glaucophane—rare Colorless garnet—rare Rutile—rather rare Brown hornblende—rare
“The grains range from about .005 to .03 mm. in diameter, averaging about .01 mm. The sorting is good. The grains are angular, and the feldspar is fresh.” (G. A. Macdonald).
No. 17. Pliocene. Paradise Valley, San Diego County, California. Just E-NE on hill on road to Aloha. L. G. Hertlein and U. S. Grant, 1v, collectors. August 13, 1937.
“Pebbly arkosic sandstone. Microscopically, it consists largely of quartz, with abundant orthoclase, and acid plagioclase (some grains partly sericitized). Smaller amounts of biotite, magnetite, microcline and muscovite included in some of the quartz grains. The cement is silica. The grains are surrounded by a narrow rim of opal, and the interspaces are filled with fibrous chalcedony.” (G. A. Macdonald).
No. 18. Pliocene. Loc. 417 (S.D.S.N.H.). Eight feet below fossiliferous conglomerate. Near International Boundary. L. G. Hertlein and U. S. Grant, 1Vv, collectors. August 14, 1937.
LIGHT MINERALS:
Quarta yen nearer re rene ee ER a cle
Orthoclase
Oligoclase
AXcidiandesitie seen steer Ea tel tf 4.9%
AL bike pect oid eee on ee eee ere ee 2.0% FIRAVY MINERALS ¢2) oe ete eee tens Mune tN 11.1%
Magnetite—rare
Ilmenite—moderately abundant Brown biotite—abundant Green hornblende—abundant Titanite—moderately abundant Zircon—moderately abundant Actinolite—moderately abundant Epidote—rather rare Zoisite—rather rare Rutile—rather rare
Brown hornblende—rare Colorless garnet—rare
“The grains range in size from that of silt up to about .07 mm. in diameter, most of them lying between 005 and .07 mm. They average about .04 mm. This sorting is moderately good. The grains are largely angular, with some subangular. The orthoclase is partially kaolinized.
“Epidote and zoisite are present in the Pliocene samples, and may have been derived from the older Eocene sediments. However, the presence of abundant hornblende and actinolite, and less abundant glaucophane, biotite, and other minerals not present in the Eocene sand examined indicate an additional source for much of the Pliocene sediment. Glaucophane, of course, indicates a Franciscan derivation; but whether the mineral was derived directly from its Franciscan source, or from older sandstone, is impossible to state.” (G. A. Macdonald).
A number of years ago brick was manufactured on a small scale in the canyon now traversed by Reynard Way. This location is definitely in the Pliocene sediments which are fossiliferous nearby.
VotumeE II] MarINE PLIOCENE OF SAN DIEGO, CALIFORNIA
Zocer7e-P/iocere
on p J
IN| g
8 G G 5 g & NK E
DIAMOND
South of this point Pliocene covered hy beach sand except for a small expos- ure here
GARNET SPFIEAL. GARNET $ ST August /928 =
Text Fic. 5. Sketch map of a part of Pacific Beach showing the location of the Pliocene exposures in the beach bluffs.
Dp)
56 San Dieco Society oF Natura History [Memorrs
The National Brick Company of National City operates on about 13 acres in a Pliocene area. However, most of the brick and tile plants utilize Eocene sediments, as related under our discussion of the Eocene.
PACIFIC BEACH AND SOLEDAD MOUNTAIN
Probably the best known section of the San Diego formation is that exposed at Pacific Beach. There the