GEOLOGY AND OIL RESOURCES ALONG THE SOUTHERN BORDER OF SAN JOAQUIN VALLEY, CALIFORNIA By H. W. HOOTS ABSTRACT The region described in this report includes a foothill belt of the San Emigdio and Tehachapi Mountains along the southern border of San Joaquin Valley., The belt displays portions of the rugged granitic cores of the moun tains and alSO rocks Of Eocene, Oligocene, Miocene, Pliocene, and Pleistocene age. Although there is thus a complete representation of the geologic series from the Eocene to the Pleistocene, some portions of the different series are wanting because of major faults and overlaps. The thickness of the Tertiary rocks (Eocene to Pliocene) varies considerably but has a maximum of about 29,000 feet. Miocene and Pliocene rocks cover most of the area investigated. The San Emigdio and Tehachapi Mountains form a structural and physio graphic link that connects the Coast Range on the west with the Sierra Nevada on the east. In these mountains there is a gradual eastward transition from the complex folds and faults of the Coast Range to the comparatively simple, gently dipping monocline of the west flank of the Sierra Nevada. The complex structural features in the San Emigdio foothills west of Grapevine Canyon and north of the San Andreas fault provide evidence that this portion of the area has been deformed by stresses with major lateral components from the south stresses which have been responsible for thrust faulting and the development of asymmetrical and overturned folds. Much of the present height of the foothill belt of the San Emigdio and Tehachapi Mountains has been produced by uplift since the beginning of Pleistocene time. Wheeler Ridge is at present the only oil-producing area along the southern border of San Joaquin Valley. Three other areas, however, appear worthy of consideration for the drilling of test wells namely, (1) a partly buried struc tural feature, possibly an anticline, 1 mile northwest of the mouth of San Emigdio Canyon; (2) the structural terrace that forms the eastern extension of the San Emigdio anticline, near Pleitito Creek; (3) the Tejon Hills. INTRODUCTION LOCATION AND EXTENT OF AREA The belt of Tertiary rocks described in this report is exposed along the southern border of the Great Valley of California between the Temblor Kange on the west and the Sierra Nevada on the east. These rocks form the northern foothills of the San Emigdio and Tehachapi Mountains and extend northward to form the Tejon Hills, which flank the south end of the Sierra Nevada. The Tejon Hills are geologically similar to the indistinct foothill belt farther north 243 244 CONTRIBUTIONS TO ECONOMIC GEOLOGY, 1929, PART II that borders the eastern edge of the San Joaquin Valley. Their geologic structure is radically different from that of the Coast Ranges and the San Emigdio foothills', but they may be considered an integral part of the structural system that extends eastward Area mapped and dis cussed in this report n which reports have already been published Other oil-producing dis tricts of the State INDEX TO PUBLISHED REPORTS ON OIL 1 San Joaquin Valley north of Coalinga (Bull.603) PPrriieesstt VVaallllee y (Bull. 581) Coalinga (Bull. 398) 4 Salinas Valley- Parkfield (8ull.69l) 5 Northwestern Kern County (Bulls,72l and 406) McKittrick-Sunset( Bull. 406) 7 Sunset-Midway (Prof. Paper 116 and 8ull47l) 8 Cuya i Valley (Bull.621) 9 Santa Maria (Bull.3Z2) 10 Summer-land) Bull.3EI) 11 Santa Clara River valley(Bull.309) IZ Simi Valley(Bull.69l) 13 LosAngeles(Bull.309) 14 Puente Hills (Bull.309) 15 Barstow-Kramer(Bull.54l) 16 LosAngeles-VenturaCBul 1.753) 17 Puente Hills(final. report, Bul!.768) 18 Southern border of,San Joaquin Valley CBull. 812D) FlGUKH 7. Index map of southern California, showing oil fields considered in reports published by the United States Geological Survey from the Temblor Eange around the south end of the Great Valley to the Sierra Nevada. In brief, it may be said that this belt of Tertiary rocks around the south end of San Joaquin Valley forms a connecting link between two major geologic provinces of Cali- GEOLOGY AND OIL, SOUTHERN SAN JOAQUIN VALLEY, CALIF. 245 fornia, provinces whose geologic characteristics are profoundly different. The area covered by this investigation, which is shown in Figure 7, lies east of Santiago Creek, a stream that enters San Joaquin Valley just east of its southwest corner. Although the western part of this belt the San Emigdio foothills between Santiago and Grape vine Creeks was previously mapped by R. W. Pack and discussed in Professional Paper 116, the hopefulness for future oil production from this district has led to a resurvey of the northern or outermost portion of the San Emigdio foothills. The entire belt is 1 to 6 miles in width and extends eastward to the Sierra Nevada, a distance of over 30 miles, and thence northward along the east edge of San Joaquin Valley for about 10 miles. This belt of Tertiary rocks, in addition to having one small oil field on Wheeler Eidge, whose daily output was about 1,000 barrels a day in April, 1927, forms a partial physiographic connection be tween two of the major oil districts of California the Sunset- Midway field, west of the area here described, and the Kern River- Poso Creek fields, north of the area. EARLIER PUBLISHED INVESTIGATIONS It appears that W. P. Blake, geologist for the Pacific Railroad Survey, was the first to record geological observations at the south end of San Joaquin Valley. In 1854 the Survey party with which Blake was connected camped near Old Fort Tejon, in Grapevine Canyon, which was then known as the Canada de las Uvas. Fossils collected by Blake in this vicinity were submitted to T. A. Conrad, who pronounced them to be Eocene. Blake's account of his investi gation,1 together with Conrad's report on the fossils,2 was published in 1857. In 1865 J. D. Whitney,3 in charge of the first Geological Survey of California, published a brief account of observations by him and his assistants in the foothill belt along the southern border of San Joaquin Valley. Fossils similar to those found by Blake were col lected in the Canada de los Alisos (now known as Live Oak Canyon) and were determined by W. M. Gabb to be Cretaceous and not Eocene, as previously reported by Conrad, a conclusion which has since proved to be erroneous. The first published account of the systematic geology and possible oil resources of the south end of San Joaquin Valley was that by 1 Blake, W. P., Geological report: U. S. Pacific R. R. Expl., vol. 5, pt. 2, pp. 41-50, 163-164, 197-211, 1857. 3 Conrad, T. A., Description of the fossil shells : Idem, pp. 317-318. 8 Whitney, J. D., California Geol. Survey, vol. 1, pp. 186-197, 1865. 246 CONTRIBUTIONS TO ECONOMIC GEOLOGY, 1929, PART H Kobert Anderson,4 although unpublished investigations of parts of the region had previously been made by Ralph Arnold, H. R. John son,5 R.. W. Pack, and others. Anderson, whose investigation was of a strictly reconnaissance nature, subdivided the Tertiary forma tions into two units the Tejon formation and later Tertiary (Mio cene and Pliocene) formations and discussed the general structure and the possible presence of oil in the region. In 1911 and 1912 R. W. Pack, with the assistance of A. T. Schwen- nesen and R. G. Davies, mapped the foothill belt along the north flank of the San Emigdio Mountains. Pack's description of the geology and oil prospects of this district was included in his report on the Sunset-Midway oil field.6 In this investigation Pack recog nized all the major stratigraphic units except the Meganos (middle Eocene), but, for convenience in mapping, grouped Oligocene strata with the lower Miocene Vaqueros formation. B. L. Clark 7 has since studied the Eocene sediments of the San Emigdio region and has subdivided them into the Meganos (middle Eocene) and the Tejon (upper Eocene). Wagner and Schilling8 have separated the Oligocene deposits from the overlying Vaqueros formation (lower Miocene) and have made stratigraphic and faunal studies of them. 'In the following pages further reference will be made to the preceding publications and to those concerning other faunal studies that have been made in the Tertiary beds of this district. ACKNOWLEDGMENTS In 1911 R. "W. Pack, of the United States Geological Survey, assisted by A. T. Schwennesen and J. D. Northrop, mapped the Tejon Hills and the strip of beds between the Tejon ranch and the San Emigdio foothills. Their maps and field notes have been at hand during the present investigation and have been of material assistance in completing this project, but unless otherwise noted in the text the present writer assumes full responsibility for the conclu sions presented herewith. In 1918 W. A. English, of the United States Geological Survey, compiled a geologic map from the field data accumulated by Pack and his assistants, a map which has facili tated the use of observations made by these earlier workers. 4 Anderson, Robert, Preliminary report on the geology and possible oil resources of the south end of the San Joaquin Valley, Calif.: U. S. Geol. Survey Bull. 471, pp. 106-136, 1912. 5 An abstract of Johnson's observations is included in U. S. Geol. Survey Water-Supply Papers 222 and 398. 8 Pack, R. W., The Sunset-Midway oil field, Calif.: U. S. Geol. Survey Prof. Paper 116, 1920. 7 Clark, B. L., The stratigraphic and faunal relationships of the Meganos group, middle Eocene of California: Jour. Geology, vol. 29, pp. 145-154, 1921. 8 Wagner, C. M., and Schilling, K. H., The San Lorenzo group of the San Emigdio re gion, Calif.: California Univ. Dept. Geology Bull., vol. 14, pp. 235-276, 1923. GEOLOGY AND OIL, SOUTHERN" SAN JOAQUUST VALLEY, CALIF. 247 Dr. B. L. Clark has examined and identified much of the inverte brate fossil material collected from this district. The geologic departments- of oil companies that have information concerning the surface and subsurface geology of this district have tendered valuable cooperation. Mr. G. C. Gester, of the Standard Oil Co. of California, and Messrs. E. D. Nolan and C. H. Wagner, of the General Petroleum Corporation, have furnished logs and production records of their wells in the Wheeler Ridge oil field. . Mr. J. A. Taff, of the Associated Oil Co., Mr. G. H. Doane, of the Milham Exploration Co., and officials of the Midland Oilfields Co. (Ltd.) and the Tejon-Kern Petroleum Co. have also furnished logs and other information from wells drilled within the district. Officials of the Tejon ranches have likewise furnished logs of wells which have been drilled on their property. Dr. E. F. Davis and other geologists of the Shell Oil Co. of California have kindly cooperated and tendered many courtesies during this investigation. Appreciation is expressed for the hospitality of employees of the General Petroleum Corporation's Eose pumping station, and to Mr. Fred Rush and officials of the Kern County Land Co. for providing living-quarters during a part of the time occupied in field work. The writer wishes to acknowledge his indebtedness to numerous geologists who have offered suggestions and have discussed observed phenomena and theoretical questions concerning this complicated dis trict. Especially is he indebted to Dr. R. D. Reed, Dr. J. P. Smith, Mr. B. F. Hake, Dr. B. L. Clark, Dr. Gerhard Henny, Mr. L. M. Clark, Mr. W. A. English, Mr. W. D. Kleinpell, Dr. W. S. W. Kew, and Mr. P. C. McConnell. FIELD WORK Field work was begun in July, 1924. During that season Wheeler Ridge and adjoining areas were mapped by plane-table triangula- tion on a scale of 2 inches to the mile and mapping on a topographic base enlarged to 2 inches to the mile was extended westward to San Emigdio Creek and southward to include the Pleito Hills. In April and May, 1926, mapping on an enlarged topographic base was con tinued westward from San Emigdio Creek to Santiago Creek and eastward from Salt Creek to and beyond Comanche Point. STRATIGRAPHY Except for the pre-Tertiary batholith of granodiorite and other closely associated rocks of igneous and metamorphic origin, the rocks of the section along the southern border of San Joaquin Valley are entirely of Tertiary age. (See pi. 31.) All parts of the Tertiary system beginning with middle Eocene are represented, and the total 248 CONTRIBUTION'S TO ECONOMIC GEOLOGY, 1929, PART II maximum exposed thickness of these deposits aggregates approxi mately 24,000 feet. Most of the section is composed of clastic sedi ments of marine origin, but continental deposits occur in the lower Miocene and in the Pliocene and Pleistocene, and basaltic and an- desitic lava and pyroclastic deposits occur in the lower Miocene. In addition, a bed of bentonite that represents a decomposed layer of volcanic ash appears to lie within the upper Eocene. BASEMENT COMPLEX The San Emigdio and Tehachapi Mountains connect the Coast Ranges with the Sierra Nevada and adjoin the broad San Joaquin Valley to the north. Their central granitic core is continuous with that of the Sierra Nevada and in this region represents one or more batholithic intrusions of pre-Tertiary age. In the northern Sierra, where Mesozoic sediments are associated with the granodiorite, there is evidence that the intrusion occurred during or at the end of late Jurassic time. It is uncertain, however, that the San Emigdio-Teha- chapi mass was developed at the same time. It is conceivable that this enormous linear intrusion was a progressive action and that, in stead of producing a single unit, it actually gave rise to a series of intrusive bodies of slightly different age. The southern or San Emigdio-Tehachapi portion may thus be either older or younger than the granodiorite of the northern Sierra and may well be of pre- Jurassic or Cretaceous age. From its relation to associated rocks ex posed along its flanks this southern intrusive mass is regarded merely as pre-Tertiary. Although granodiorite is by far the most common rock type in the San Emigdio and Tehachapi Mountains, the mass is far from uniform in petrographic details and grades from gray and pink granite with a comparatively small amount of ferromagnesian minerals to black diorite. This granitic mass is gneissic in part and is associated with a metamorphic series that consists largely of gneiss and schist but includes a relatively small amount of coarsely crystal line limestone. EOCENE BOCKS MEGANOS FORMATION (MIDDLE EOCENE^, The presence of rocks in the San Emigdio foothills containing what was believed to be a Meganos (middle Eocene) fauna was first recognized by B. L. Clark.9 These rocks, which had previously been included with the overlying Tejon formation, were traced by Clark from a point just west of San Emigdio Creek eastward to 9 Clark, B. L., The stratlgraphic and faunal relationships of the Meganos group, middle Eocene of California: Jour. Geology, voL 29, pp. 145-154, 1921. GEOLOGY AND OIL, SOUTHERN" SAW JOAQUEST VALLEY, CALIF. 249 Grapevine Canyon. Clark10 has more recently concluded that these fossiliferous beds east of San Emigdio Canyon should be referred to the horizon that he has named Domengine. These rocks east of San Emigdio Canyon have not been studied in detail by the present writer, but according to Clark they are best exposed between Pleito and San Emigdio Canyons, where " the basal beds consist of several hundred feet of fairly indurated coarse reddish-gray arkosic sand stone. The upper part of the section is composed principally of sandy shales and platy shaly sandstone.11 Large angular boulders of granite also occur at the base of the Eocene section in San Emigdio Canyon. The Meganos formation is described by Clark as resting directly upon the granite and is reported by the same writer to be overlain unconformably by the Tejon formation (upper Eocene). He says:12 One of the localities where the unconformable contact between the Meganos and the Tejon may be seen distinctly is about one-eighth of a mile back of the old Douglas ranch house, in the main canyon of San Emigdio Creek (near the south edge of the NW. % sec. 5, T. 9 N., R. 21 W.). Here the contact is beautifully exposed on the side of the canyon. There is a difference in dip between the two series of as much as 10°. A basal conglomerate containing fossiliferous boulders derived from the beds below was found along the con tact.18 * * * At the locality just mentioned the Meganos beds have a thickness of less than 15 feet, and not more than 300 feet to the west the basal conglomerate of the Tejon rests on the granite. Just back of the ranch house, a little far ther west, a remnant of the basal Meganos sandstone outcrops below the basal conglomerate. Here the unconformity is evident. Traced east of this locality, the Meganos beds are found to thicken rapidly, reaching their maximum thick-» ness near the head of Pleito Canyon about 3 miles to the east, where the Meganos beds have an estimated thickness of more than 1,000 feet. These beds thin out rapidly farther east, and in the canyon of Salt Creek, only a little more than 4 miles distant, their thickness probably is not more than 100 feet. The conglomerate of the basal Tejon was traced to Tecuya Creek in the next large canyon east of Salt Creek. In Grapevine Canyon the basal conglomerate of the Tejon was found to be separated from the granite by about 25 feet of unfossiliferous coarse arkosic sandstone, together with a few feet of dark shales. Thus the beveled Meganos is transgressed by the Tejon from west to east in the vicinity of Grapevine Canyon, only a very small part of the Meganos being left, and in the next canyon to the east of Live Oak Canyon the Meganos beds fail to appear. 10 Clark, B. L., The Domengine horizon, middle Eocene of California: California Univ. Dept. Geol. Sci. Bull., vol. 16, p. 107, 1926. "Clark, B. L., op. cit. .(Jour. Geology), p. 152. MIdem, pp. 149-152. 13 The present writer has examined the exposure in the east wall of San Emigdio Canyon illustrated by Clark and is not certain that the apparent structural discordance in this exposure indicates a period of uplift between Meganos and Tejon times. The beds are very lenticular, and it seems at least possible that the observed phenomenon is the result of normal deposition by currents in shallow water conditions under which these basal Eocene sediments may well have accumulated. 250 CONTRIBUTIONS TO ECONOMIC GEOLOGY, 1929, PABT H As a result of more recent fossil collections from this district. Clark * has concluded that his Meganos formation as described above includes beds which are actually equivalent to his Domengine formation north of Coalinga. His statement is as follows: 14 Later work on the Eocene fauna from San Emigdio Canyon, listed by the writer in the 1921 paper as coming from the Meganos, shows that it probably should be referred to the Domengine horizon. However, to the west of San 4- Emigdio Canyon in the eastern branch of San Diego [Santiago] Canyon what appears to be a good Meganos fauna was found near the base of the Eocene and only a little distance above the granite contact. Here Turritella merriami and several other distinctive Meganos species were collected. No stratigraphic work has been done in differentiating these two horizons in this region. Clark now considers that the Meganos formation extends eastward to the vicinity of Salt Creek and that only his Domengine formation and the Tejon are present farther east in Grapevine Canyon.15 It should be noted that all fossils thus far reported from the struc turally complicated Eocene east of Salt Creek have been referred to the Tejon by different workers. On the east bank of Los Lobos Creek, just below the road crossing near the granite contact, Eocene beds of probable Meganos age crop out in a small but prominent hill and consist of well-bedded brown and greenish-gray sandstone and sandy shale that are conglomeratic in part and contain angular boulders of dark gneiss and schist 1 to 5 feet in diameter. (See pi. 32, A.) These beds are fossiliferous, but the forms collected were too poorly preserved for identification. Similar well-bedded brown sandstone and shale appear farther west, "near the granite contact, where they dip either northward at an angle of about 75° or southward toward the granite. TEJON FORMATION (UPPER EOCENE) PALEONTOLOGIC STUDIES The richly fossiliferous Eocene beds of the Tejon formation between Live Oak Canyon and San Emigdio Creek have furnished material for study by many investigators since they were first dis covered in 1854 by Blake.16 The first Eocene fossils reported from California came from Grapevine Canyon, and, as determined by sub sequent investigations, this and adjoining localities contain an unusu ally rich marine invertebrate fauna that makes up a distinct faunal unit of the California Eocene. The linear outcrop of these rocks, in the vicinity of Live Oak, Grapevine, and Tecuya Creeks is thus the- type locality of the Tejon formation, the name Tejon having been 14 Clark, B. L., The Domengine horizon, middle Eocene of California: California Univ. Dept. Geology Bull., vol. 16, p. 107, 1926. 16 Personal communication, October, 1926. i« Blake, W. P., TJ. S. Pacific R. R. Expl., vol. 5, pp. 41-50, 163-164, 197-211, 1857. GEOLOGY AND OIL, SOUTHERN SAN JOAQUIN VALLEY, CALIF. 251 h'rst applied to these sediments by Gabb " from their occurrence near old Fort Tejon. Much recent work has been done on the paleontol ogy of the Tejon, and the last and most comprehensive study of the fauna of this formation is that by Anderson and Hanna.18 SAN EMIGDIO CANYON In the vicinity of San Emigdio Canyon only the upper 800 feet of the Tejon formation was examined. This part of the formation on the north limb of the Devils Kitchen syncline supports an unusually sparse vegetation and consists of numerous thin slabby brown and gray sandstones of fine texture that are intercalated with purplish- gray and brown shale and sandy shale and very hard thin yellowish- brown. nodular beds of iron carbonate. Some of the slabby sand stones have ripple-marked surfaces, but others are finely conglomer atic, with well-rounded pebbles. The sandstone of the upper 300 feet of the Tejon formation at this locality is more massive and occurs in beds from 1 to 4 feet thick, in contrast to the thin slabby sandstone of the underlying portion. Poorly preserved invertebrate fossils and abundant plant fragments were found near the top of the formation. The lithology of the upper part of the Tejon formation in San Emigdio Canyon differs from that of the overlying San Lorenzo formation (Oligocene) in that it is comparatively thin-bedded throughout, with no unusually massive beds of sandstone, and that shale is the preponderant type of rpck. No conglomerate or sugges tion of unconformity could be found at the top of the Tejon forma tion in this vicinity. EAST OF SALT CREEK In some localities east of Salt Creek the Tejon formation rests upon the granite or upon a slight thickness of beds belonging to the Domengine formation of B. L. Clark that are believed by him to crop out below the Tejon formation east of Salt Creek. At other localities these Eocene rocks are faulted against the granite. The Tejon is overlain unconformably by the Vaqueros formation (lower Mio cene). The Tejon-Vaqueros contact is well exposed at several locali ties, and east of Salt Creek, although there is no noticeable angular discordance, marine Oligocene strata are missing, and a coarse con glomerate of the Vaqueros rests directly upon the Tejon formation. The outcrop of the Tejon formation between San Emigdio and Salt Creeks was not examined during this investigation but is well 17 Gabb, W. M., Cretaceous and Tertiary fossils: California Geol. Survey, Paleontology, vol. 2, p. 13 of preface, and footnote on p. 129, 1869. 18 Anderson, P. M., and Hanna, G. D., Fauna and stratlgrapbic relations of the Tejon Eocene at the type locality in Kern County, Calif.: California Acad. Sci. Occasional Paper 11, 1925. 3415G0 30 17 252 CONTRIBUTIONS TO ECONOMIC GEOLOGY, 1929, PART H described by Pack,19 who states that its greatest thickness, approxi mately 4,300 feet, occurs near Pleito Creek, where it consists of shale, sandstone, and some conglomerate. This thickness, however, in cludes the Meganos formation, which, according to Clark,20 is more than 1,000 feet thick. The Tejon formation thins markedly both to the west and to the east of this locality; near Live Oak Creek, 13 miles east of Pleito Creek, it has a thickness of about 1,200 to 1,500 feet, but it decreases eastward until, at a point 5 miles distant, it is completely overlapped by the overlying Miocene deposits. Between Salt and Live Oak Creeks the Eocene sediments are so greatly de formed and duplicated by faulting and folding that their thickness can not be accurately determined. West of Grapevine Creek Eocene sediments within 100 to 200 feet of the granite consist entirely of brown shale and fine sandy shale and, at several well-exposed places, dip southward toward the granite at angles commonly less than 50°. It seems certain that Eocene sediments in this vicinity are in fault contact with the granite, a condition that may exist throughout parts of the district farther west. In the vicinity of Tecuya Creek and Grapevine Canyon the Tejon formation (with possibly a slight thickness of the upper Meganos), consists in greater part of soft dark-brown, dark-gray, lavender, and greenish-gray shale and sandy shale. Associated with the shale is considerable poorly cemented soft gray and brown sandstone, and much of the section contains numerous hard brown sandstone concre tions that resemble cannonballs, many of which are fossiliferous. More abundant well-preserved fossils commonly occur in thin lenticu lar beds of hard brown sandstone. A concretionary bed of gray limestone 1 foot thick was noted in Grapevine Canyon, and round limestone concretions are fairly common. Brown sandstone conglomerate occurs 500 feet or more above the base of the Eocene series on the east side of Grapevine Canyon and also just west of Tecuya Creek; the cobbles in this conglomerate are subangular, are 8 inches or less in diameter, and consist of gray granite, diorite, gray and pink quartzite, felsite porphyry, dark-gray flint, fine and coarse gray sandstone, and light-gray limestone. Near the base of the Eocene in the west wall of Grapevine Canyon cobbles and boulders of similar petrographic character range from rounded to subangular and are as much as 12 inches in diameter. In Live Oak Canyon the upper 100 feet of the Tejon formation consists of soft brown sandstone, with only a small amount of shale 18 Pack, R. W., The Sunset-Midway oil field, Calif.: U. S. Geol. Survey Prof. Paper 116, pp. 23-25, 1920. 20 Clark, B. L., The stratigraphic and faunal relationships of the Meganos groups middle Eocene of California : Jour. Geology, vol. 29, p. 152, 1921.