754 INDEX TO THE STRATIGRAPHY OF NORTH AMERICA. 



and a period of shallow-water conditions with which the Vaqueros began. The conglomerate 

 gives place in turn to more shale and sandstone, which continue to the summit of the terrane. 

 At the top there is a conformable gradation into the Monterey (middle Miocene) beds, the 

 summit of the Vaqueros being marked by a calcareous zone in many places — as, for instance, 

 southwest of Lompoc, where the two formations are divided by a very prominent exposure 

 of hard limestone. 



In the hills west of Tulare Lake lies the Coalinga oil district, studied by Arnold 

 and Anderson/^" who tentatively assigned to the Tejon formation a series of beds 

 described as follows : 



The formation mapped as the Tejon in the Coalinga district is made up entirely of sedi- 

 mentary strata that dip toward the great valley in the monocline along the eastern flank of 

 the mountains and are exposed on the surface in a narrow discontinuous belt between the 

 Cretaceous beds which underlie them and those of the Miocene which overlie them. The beds 

 so mapped have a thickness of 1,600 to 1,850 feet and are divisible into two main members of 

 approximately equal thickness — a lower one consisting of sandstone in the southern part of the 

 district and of dark clay shale and sand in the northern part, which is certainly of Eocene age, with 

 the possible exception of a small thickness at the base, and an upper one of light-colored organic 

 shale which affords few species of fossils and no conclusive evidence as to its age. This upper 

 member may represent either Eocene or Oligocene time, but the facts that there seems to be a 

 gradation from the beds of the lower member into those of the upper and that the two invariably 

 occur together in this region favor its assignment to the Eocene. It is made up of thin beds 

 of whitish and purplish siliceous, argillaceous, and Ideally calcareous shale, which is easily 

 recognizable and which lends individuality to the formation. The shale is very similar, especially 

 in some places, as north of Coalinga, to the sihceous shale of the. formation along Reef Ridge 

 that is described later as the Santa Margarita ( ?) formation, and the two must not be confused : 

 It is also somewhat similar to the purple shale of the upper Chico. Where the Tejon formation 

 is thick, shale and clay form a greater proportion of the whole than the sandstone, but a great 

 local variation in the thickness of this member is noteworthy because due to the great uncon- 

 formity between it and the overlying Miocene beds. A large portion of the formation had been 

 worn away before the Vaqueros (lower Miocene) sandstone was deposited on its upturned 

 surface. It is possible that an unconformity occurs within the beds mapped as Tejon at the 

 base of the upper shale, but no discrepancy in dip between the beds of the two divisions has 

 been found, and the succession of beds is seemingly continuous. 



As already pointed out, an unconformity exists between the Chico (Upper Cretaceous) and 

 Tejon (Eocene) beds, in spite of the facts that no sharp line of demarcation is to be drawn 

 between the Tejon and the underlying Chico in the northernmost part of the district and that 

 there appears to be a gradation from the beds of the former into those of the latter, as if they 

 had been formed during a continuous period of sedimentation. In the southern portion of the 

 district the Tejon overlies unconformably beds that belong to an earlier portion of the Creta- 

 ceous, either lower Chico or KnoxvUle, thus proving that a period of land conditions and erogenic 

 disturbances preceded the Tejon. 



Tejon group was the name applied by J. D. Whitney to the fossiliferous strata in the vicinity 

 of Fort Tejon, Kern County, and IMartinez, Contra Costa County, which were included by Gabb 

 under his division B, or Upper Cretaceous." As the result of later studies the fossils of this 

 formation are now considered to be of Eocene age. Strata of the same age occur extensively 

 in the region of Carq'uinez Straits, east of Mount Diablo, and have been found at a number of 

 different points along the western border of the San Joaquin Valley, notably at New Idria and 

 in the region discussed in the present paper. 



For a general correlation table of the Tertiary formations of the California 

 Coast Range see Chapter XVII (p. 818). 



oGeol. Survey California, Paleontology, vol. 2, 1869, preface, p. xiii. 



