1917] Nomland: Fauna of the Santa Margarita Beds 297 



Arnold and Anderson,* and by Anderson and Pack, the Santa Mar- 

 garita sandstone is continuous as a thin series of beds flanking the 

 eastern slopes of the Diablo Range from near the town of Oilfields 

 to a short distance north of Arroyo Honda. The formation is thus 

 exposed for a length of somewhat more than twenty miles, being 

 apparently overlapped in both the northern and southern ends by 

 the younger Etchegoin. Another small exposure of the same forma- 

 tion composed of fossiliferous sandstone is also found a few miles 

 northwest of Coalinga. 



Considered as a whole, the Santa Margarita is decidedly distinct 

 from the adjoining formations. At some localities, due to the simi- 

 larity of lithology of the Santa Margarita near the base of the 

 underlying lithologic member called the Big Blue, the line of con- 

 tact is traced with difficulty. The Big Blue was therefore tentatively 

 mapped with the Santa Margarita by Arnold and Anderson. The 

 more recent work of Anderson and Pack 10 in the area north of the 

 Coalinga district has shown that the Big Blue belongs with the 

 Vaqueros and that it is unconformably related to the Santa Mar- 

 garita. The Big Blue consists largely of deposits of serpentine detri- 

 tus in part at least of land-laid origin. In the Coalinga district it is 

 highly colored and is barren of marine invertebrate fossils. In the 

 area north of the Coalinga district, however, Anderson and Pack 

 report the finding of marine fossils in this member. 



The Santa Margarita is similarly decidedly distinct from the 

 overlying Etchegoin. As already stated by the writer elsewhere, 11 

 there appear to be good reasons for believing that the contact between 

 the Santa Margarita and the Etchegoin is about two hundred feet 

 stratigraphically lower than the line mapped by Arnold and Ander- 

 son. The beds containing fossil remains of the Pliocene horse Neo- 

 hipparion inolle Merriam would thus be included with the Etchegoin 

 instead of the Santa Margarita. This will therefore be used as the 

 base of the Etchegoin in the present paper. As thus defined, the 

 beds lying immediately above the Santa Margarita have a number 

 of characteristics indicative of terrestrial deposits. These beds are 



s Arnold, Ralph, and Anderson, Robert, Geology and oil resources of the 

 Coalinga district, etc. 



9 Anderson, Robert, and Pack, Robert W., Geology and oil resources of the 

 west border of the San Joaquin Valley, etc. 



10 Op. cit., p. 92. 



11 Nomland, J. O., Relation of the invertebrate to the vertebrate faunal zones 

 of the Jacalitos and Etchegoin formations in the north Coalinga region, Califor- 

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



