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University of California Publications. [Geology 



The San Pablo beds in middle California appear to be repre- 

 sented by beds of equivalent age in other parts of the Coast 

 Ranges. To the south of San Francisco Bay several formations 

 have been described which resemble very closely both in their 

 physical characteristics and in the fauna contained in them, the 

 San Pablo beds in the bay region. In the Mount Diablo Range, 

 Anderson has named and described the Etchegoin beds which 

 extend over a large area and possess an immense thickness. They 

 too lie unconformably upon all the underlying formations. Im- 

 mediately below the Etchegoin beds are the Coalinga beds which 

 he considers to be older than the San Pablo and younger than 

 the Monterey. If so, the Coalinga beds represent a period of 

 sedimentation between the close of Monterey time and the be- 

 ginning of the San Pablo. No such beds appear in middle Cali- 

 fornia, but a time interval is indicated by the unconformity be- 

 tween the Monterey and San Pablo in the San Pablo Bay region. 

 The lower portion of the Etchegoin beds or rather the Etchegoin 

 sands he considers as the equivalent of the San Pablo beds at 

 San Pablo Bay. This portion is composed of unconsolidated 

 sands or gravels in which a characteristic blue or gray color 

 predominates. The sands have in general a coarse pebbly texture 

 often forming beds of conglomerate and in many cases having 

 the appearance of volcanic ash. The following are some of the 

 more important characteristic San Pablo fossils which occur in 

 the Etchegoin formation : 



Pseudocardium gabbi. Macoma nasuta. 



Neverita recluziana. Trophon ponderosum. 



Nassa calif ornica. Tapes staleyi. 



Astrodapsis tumidus. Macoma secta. 



A comparison of the Etchegoin fauna shows many of the 

 species to be similar to those of the San Pablo and it thus seems 

 best to correlate them as being equivalent in age. 



In the Salinas Valley there is a formation known as the Santa 

 Margarita composed of sandstones, shales, and conglomerate. 

 Sandstones appear to predominate. This entire series was con- 

 sidered by Dr. Fairbanks to represent the San Pablo. An 

 abundant fauna has been listed from here, and among the more 

 characteristic forms which occur also in the San Pablo are 



