1919] Kcw: Geology of a Part of the Satita Ynez River District 11 



sandstone so characteristic of the Tejon throughout the State. It 

 usually forms bluffs and for this reason this lithologic member is often 

 referred to as the "bluff sandstone." Its thickness here is about 500 

 feet. West of Oso Creek the bluff sandstone lies in a shallow syncline 

 and forms vertical cliffs equal in height to its thickness. Another 

 feature of the bluff sandstone is its cavernous weathering and nodular 

 appearance. The character of the sandstone is that of a beach sand 

 and for the most part is composed of medium-sized to coarse quartz 

 grains. It is clean, well sorted, and in some places cross-bedded. 

 A thin-bedded, fine-grained, easily weathered, buff to brownish colored 

 sandstone about 1350 feet thick, containing minor amounts of clay 

 shale, overlies the bluff sandstone. The only exposure of this member 

 within the area mapped is located in the axis of the syncline west of 

 Oso C-reek, where it has been preserved from erosion. 



In the Santa Ynez Mountains within the area studied, the Eocene 

 section consists of about 14,000 feet of strata which is far thicker than 

 the section west of Oso Creek. Arnold® measured a section east of 

 Summerland which is over 8700 feet thick, not including the basal 

 beds. The lowest beds exposed in this region are massive liard, brown, 

 well-indurated sandstone, at the base of which is a heavy layer of 

 conglomerate about 150 feet thick, made up mainly of quartzite 

 boulders. This conglomerate is followed by a thin series of soft brown 

 sandstone, which grades up into the green shale similar to that in the 

 Oso Creek section, liut harder and of a darker shade. The shale 

 member here as in the latter place is overlain by the massive brownish 

 bluff sandstone which forms the greater part of the Santa Ynez Moun- 

 tains from La Cumbre Peak west to San Marcos Pass and beyond. 

 This section is well shown on the Cold Spring trail and Arroyo Burro 

 trail from Santa Barbara to the Santa Ynez River. The upper 

 soft sandstone is absent from the Santa Ynez IMountains section. 

 As a whole, the Tejon formation corresponds to that given by 

 Eldridge and Arnold' for the Topatopa formation occurring in the 

 range of mountains of that name in Ventura County. The lower part, 

 consisting of about 2000 feet of "excessively hard, submassive sand- 

 stones and quartzites ' ' in the Topatopa Mountains, is not represented 

 by so great a thickness in the Santa Ynez Moimtains, but this may be 

 due to the fact that the lower beds are cut out by the Santa Ynez fault. 



8 Arnold, Ralph, Geology and oil resources of the Summerland district, Santa 

 Barbara County, California, U. S. Geol. Surv. Bull. 321, p. 22, 1907. 

 7 Op. cit. 



