466 University of California Publications in Geology [Vol. 9 



Santa Barbara Counties. This view is based upon the fact that within 

 the San Luis Quadrangle, as well as northwestward through the heart 

 of the Coast Ranges, the Eocene, or Tejon formation, is entirely absent, 

 while on the borders of the Great Valley and southward across the Coast 

 Ranges the formation is extensively developed. The Eocene, then, in the 

 region under discussion was an epoch of erosion, and it was during this 

 time that large portions of the earlier formations were removed. The 

 region was probably reduced to one of low relief, and the waste material 

 was deposited beyond the present shore line. 



Decisive direct evidence upon this question can be obtained only 

 by careful mapping of large areas. In the vicinity of Stone Canon, 

 Monterey County, the areal and structural relations of the Miocene 

 to the Franciscan and Cretaceous indicate a very great period of 

 erosion between the deposition of the Chico-Cretaceous and the Miocene 

 sediments. This is shown by the residual nature of the Chico ex- 

 posures in many places and by pre-Miocene folding. 



The fauna of the Tejon in the Coalinga District which is east of 

 the San Luis Quadrangle contains such genera as Spatangus, 

 Trochocya.thus, Balanophyllia, Turbinolia, Spisula, Turris, Fusus 

 and Surcula, in abundance. These genera are more characteristic of 

 an archipelago or open-ocean habitat than that of a sound. Such 

 genera as Barbatia, Pot amides and Corbicula do occur, but in most 

 cases strata containing such an assemblage are limited in extent and 

 probably represent estuarine deposits near the mouths of the Eocene 

 rivers. 



Kocks derived from the Franciscan, Chico, and Martinez groups 

 form the conglomerate boulders in the basal Tejon member north of 

 Mount Diablo. Their occurrence suggests the existence of a con- 

 tinental land-mass a short distance east of the present site of Mount 

 Diablo or of islands in this vicinity. The absence in this region of 

 uppermost Tejon sediments, their presence forty miles eastward, and 

 the direct field evidence in the lone facies of the Tejon Eocene which 

 demonstrates deposition along a shore line by a transgressing sea can 

 be easily explained by a great interval of erosion in post-Eocene time 

 during which all the Tejon sediments were removed from the outer 

 ranges and the uppermost sediments from the inner of the Coast 

 Range. An unconformity between the Oligocene and the Tejon at 

 Walnut Creek indicates that this condition existed, for the upper- 

 most Tejon strata contributed coal and sandstone to the basal conglo- 

 merates of the Oligocene. The Tejon was possibly exposed to subaerial 

 erosion during another long period of time which in certain places is 



