294 University of California Publications in Geology [Vol. 10 



Introduction 



Since the first description of the Santa Margarita in the San 

 Luis quadrangle by Dr. H. W. Fairbanks, the question of age of 

 this formation has from time to time attracted much attention. 

 Especially important has been the relation of the Santa Margarita to 

 the upper Miocene and Pliocene formations in the vicinity of San 

 Francisco Bay. The Santa Margarita was considered by Fairbanks 

 a division of the San Pablo, while a number of other geologists have 

 thought it older than that group. The preservation of the fossils of 

 the Santa Margarita at the type locality is very poor. Few attempts 

 have been made to list a typical Santa Margarita fauna, and correla- 

 tion with other localities has been uncertain or frequently impossible. 

 A study of the Santa Margarita fauna has therefore become highly 

 important for correlation purposes. 



The present paper is a study of a fauna collected from beds in 

 the north Coalinga region which have been correlated with the Santa 

 Margarita. The palaeontologic studies apparently indicate that these 

 beds represent the upper part of the San Pablo group. The faunas 

 also indicate that they represent at least in part the same horizon as 

 the Santa Margarita at the type locality. 



Most of the material studied from the Coalinga region was col- 

 lected by Dr. B. L. Clark during his research on the fauna of the 

 San Pablo group. The writer is much indebted to Dr. Clark for the 

 use of his field notes on the geology and for numerous valuable sug- 

 gestions, especially in regard to correlation with the San Pablo fauna. 

 Dr. R. E. Dickerson kindly permitted the writer the use of material 

 in the collections of the California Academy of Sciences, San Fran- 

 cisco. 



Previous Palaeontologic and Geologic Work 



The first published account of palaeontologic and geologic investi- 

 gation in the region north of Coalinga was included in a paper pub- 

 lished in 1905 by F. M. Anderson. 1 In this publication the Santa 

 Margarita was grouped with what he called the Coalinga Beds. These 

 beds comprised what was later mapped as Vaqueros, Santa Margarita, 

 and Jacalitos formations by members of the United States Geological 

 Survey. A brief general description of the geology with faunal lists 



i Anderson, F. M., A stratigraphic study in the Mount Diablo Eange of 

 California, Proe. Calif. Aead. Sei., ser. 3, vol. 2, no. 1, 1905. 



