200 University of California Publications in Geology [Vol. 10 



... 



upper and lower divisions of the Etchegoin. Above the Etchegoin 

 in that area are beds which have been correlated with the Tulare 

 farther east. In Priest Valley the same relationship is found as in 

 the upper part of the Waltha.ni Creek area. The lower portion of the 

 Etchegoin in that region is greatly faulted, so that the different faunal 

 horizons can be traced only with difficulty. At several localities, how- 

 ever, fossils characteristic of the lower horizons are found. What 

 corresponds to the Peeten coalingensis zone of the upper Etchegoin 

 in the Jacalitos Hills can readily be distinguished in that area. 



Southeast of the San Andreas fault the Etchegoin has not been 

 extensively mapped in this region. It is known, however, to be present 

 about one and one-half miles southeast of Lonoak. The small fauna, 

 listed in another part of this paper, indicates a probable middle Etche- 

 goin age. Also about thirty miles southeast of Lonoak, on Big Sandy 

 Creek, near the southeast corner of the Priest Valley Quadrangle, an 

 Etchegoin fauna has been obtained. In Indian Valley of the same 

 quadrangle the Pliocene is extensively developed, resting on a con- 

 siderable thickness of Santa Margarita shale. The included fauna 

 here indicates a lower Etchegoin age. It therefore appears probable 

 that the Etchegoin may be extensively developed along the western 

 slope of tlie Diablo Range. 



Relation to Adjoining Formations 

 RELATION TO THE SANTA MARGARITA 



In mapping the geology of the Coalinga district by Arnold and 

 Anderson the base of the "Jacalitos" (lower Etchegoin) in the north- 

 ern part of the region was placed at the base of a conglomerate con- 

 taining a large amount of fossil wood. This horizon is about five 

 hundred feet above the uppermost fossiliferous Santa Margarita. On 

 being traced northward the thickness of the Santa Margarita grad- 

 ually grows less and these beds finally disappear. This apparent 

 overlapping has been taken as proof of unconformity between the 

 "Jacalitos" and the underlying Santa Margarita. As the writer has 

 shown in another paper, 17 there are reasons for considering that this 

 unconformity occurs about two hundred feet lower stratigraphically 

 than the position at which it was placed by Arnold and Anderson. 

 The difference in the fauna between the lower Etchegoin and the 

 Santa Margarita is such that a long time must have elapsed or a 



it Univ. Calif. Publ. Bull. Dept. Geol., vol. 9, no. 6, 1916. 



