296 University of California Publications in Geology [ VoL - 10 



The most recent report on the geology of this section of the 

 state is on the region north of the Coalinga district by Robert Ander- 

 son and Robert W. Pack. 7 The Big Blue is not included with the 

 Santa Margarita, but is regarded as Vaqueros, this being based on 

 fossils found in the region studied. The Santa Margarita is consid- 

 ered older than the San Pablo. 



Relation to Other Formations 

 The Santa Margarita formation of the San Pablo group as mapped 

 in the Coalinga district is found in two areas. The lithology of these 

 two regions is decidedly different. West and southwest of Coalinga 

 the formation consists almost entirely of a light-colored diatomaceous 

 shale. This shale in many characteristics is very similar to the 

 Monterey Shale found in many parts of the Salinas Valley. At 

 some localities west of Coalinga a thin basal sandstone is found con- 



Horizontal Distance represented about t Mttett 



Fig. 1. Generalized section across formations on east side of Diablo Range, 

 northeast of Coalinga. Kck, Cretaceous; Ttj, Tejon (Eocene); Tel, Oligocene; 

 Tt, "Temblor" (Miocene); Tsm, Santa Margarita (Miocene); Te, Etciiegoin 

 (Pliocene) ; Tpr, Tulare (Pliocene) ; Qual, Pleistocene and Recent alluvium. 

 (After Ruckman.) 



formably below the shale. From this member a small fauna has been 

 obtained, which is the chief evidence favoring inclusion of this sand- 

 stone and the shale above with the Santa Margarita. The shale west 

 and southwest of Coalinga rests with large discordance in dip on the 

 Vaqueros and is overlain unconformably by the Etchegoin. In the 

 other area which is found north and northeast of Coalinga, the Santa 

 Margarita is lithologically quite different from the diatomaceous 

 shale. The formation here consists entirely of soft yellowish sand- 

 stone which in many localities is highly fossiliferous. It is the fauna 

 obtained from this area of Santa Margarita which will be described 

 in the present paper. 



As shown by the mapping of the region north of Coalinga by 



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

 west border of the San Joaquin Valley north of Coalinga, California, U. S. Geol. 

 Surv. Bull. 603, 1915. 



