1916] 



Dickerson: Tejon Eocene of California 



467 



represented by unconformity between the Miocene and Cretaceous. 

 Both time-intervals were apparently very long ones. They were so 

 long that but few Tejon species persisted into the Oligocene, and 

 none into the Miocene. When one remembers that the Tejon fauna 

 contains at least 300 to 400 mollusca, the length of time represented 

 by these two unconformities is quite sufficient to account for the re- 

 moval of the Tejon by erosion from the present sites of the moun- 

 tains bordering the Pacific. The distribution of Tejon sediments, the 

 absence of the Siphonalia sutterensis zone in the Mount Diablo region, 

 the presence of a typical marine fauna in most horizons of the Tejon 

 and the existence of two periods of erosion between the Tejon and 

 Miocene, lead to the conclusions that the Tejon was deposited by a 

 transgressing sea and that Tejon sediments were largely removed from 

 the outer Coast Ranges during post-Tejon and pre-Miocene time. The 

 existence of islands upon a wide continental shelf is possible, but if 

 they existed they were not sufficient in number or extent to prevent 

 the free access of the Eocene ocean. 



GEOGRAPHY OF THE TEJON SEA 



During the whole of Eocene time in California the San Fran- 

 cisco Basin 86 was a negative area, and for this reason the Eocene 

 record of deposition is most complete in this portion of California. 

 This basin was small during Martinez time, being merely an open 

 bight extending from the vicinity of Lower Lake in Lake County 

 to about the southern boundary of San Mateo County. The most 

 easterly point in the basin in Martinez time was probably a few 

 miles east of Benicia. After the recession of the sea at the close of 

 Martinez time, mountain-making movements were moderately active 

 and the Martinez strata were folded and eroded. Again, the San 

 Francisco Basin was an area of sedimentation at the beginning of 

 Tejon time. Apparently the Eocene sea during early Tejon time 

 transgressed upon the land in the San Francisco Basin to a far 

 greater extent than during Martinez time. The Tejon sea probably 

 extended from the vicinity of Round Valley, Mendocino County, to 

 the vicinity of Coalinga. The data upon which this is based was given 

 above. During Tejon time, numerous local oscillations occurred. 

 The sedimentary record on the north and south sides of Mount 



so Dickerson, R. E., Fauna of the Martinez Eocene of California, Univ. 

 Calif. Publ. Bull. Dept. Geol., vol. 8, No. 6, pp. 69-71, 1914. 



