46 University of California Publications in Geology [Vol. 8 



land barrier, the range of mountains extending from San Gorgonio 

 Pass south into the peninsula of Lower California and commonly 

 known as the Peninsular Range. 



The age of the Carrizo formation has not been definitely deter- 

 mined. Dr. Arnold 9 referred to it as equivalent to the Upper Miocene 

 or Lower Pliocene Etehegoin formation of the San Joaquin Valley 

 of Middle California, correlating by means of the pectens. The 

 echinoderm fauna seems to indicate a comparatively late age, as several 

 of the forms are very closely related to the species living in the Gulf 

 of California at the present time, and these species are presumed to 

 change relatively rapidly. Whether this seemingly slow development 

 is due to comparative isolation in a warm-water area is as yet not 

 known. These questions can not be answered definitely until the 

 fauna has been compared carefully with the Recent life from the 

 Gulf of California. 



An approximate list of the fauna of the Carrizo formation, so far 

 as determined, is as follows : 



Lower Division Upper Division 



All Carrizo Yuha 



localities Valley Buttes 



Pelecypoda. 



Anomia subcostata Conrad 



X 



X 



X 



Anomia, n. sp 



X 



X 



X 



Area, n. sp. A 



X 



X 





Area, n. sp. B 



X 







Cardium aff. quadrigenarium Conrad 



X 







Crassatellites, sp 



X 







Divaricata eburnea Reeve 



X 







Dosinia, n. sp 



X 







Glycimeris, sp 



X 







Hinnites gigantea, n. var 



X 







Lithodomus, sp 



X 







Metis alta Conrad 



X 







Ostrea heermani Conrad 



X 





X 



Ostrea vespertina Conrad 



X 



X 



X 



Panope generosa Gould 



X 







Peeten carrizoensis Arnold 



X 



X 





Pecten subnodosus, n. var 



X 







Peeten circularis, n. var 



X 



X 



X 



Peeten deserti Conrad 



X 







Pecten cerrosensis var. mendenhalli Arnold.... 



X 







Peeten keepi Arnold 



X 







Pecten, n. sp 



X 







Phacoides, cf. sanctaecrucis Arnold 



X 







Pinna, sp 



X 







Pholas, sp 



X 







9 Arnold, Ralph, op. cit., 1910. 









