412 University of California Publications in Geology [Vol.8 



beds makes it unsafe to generalize as to its distinctness. The localities 

 from which this fauna was obtained are nos. 104, 118, and 1499. 



In general, division B of the San Pablo group on the south side of 

 the Mount Diablo anticline presents three minor faunal zones. The 

 faunas of the two lower zones, though similar, each contains a number 

 of species not common to the other. These two zones are probably also 

 represented in the San Pablo Bay section. In both sections there is 

 a change in the character of the deposits along the line of the division 

 of the zones. 



The third minor faunal zone, which so far has yielded only a meagre 

 fauna, has not been certainly recognized outside of the section on the 

 south side of Mount Diablo. 



Rocky Ridge 



A very interesting section of the San Pablo Group is seen on the 

 south side of Rocky Ridge near the southeast corner of the Concord 

 quadrangle. Here the thickness of the group is roughly estimated 

 to be twenty-four hundred feet. 



STEATIGEAPHY AND LITHOLOGY 



Relation of San Pablo to Monterey Group. — The beds of the upper 

 Monterey (Scutella breweriana zone) outcrop along the main crest 

 of the ridge, where the species Scutella breweriana is found in 

 abundance. The lower Monterey of this section has been faulted away 

 and the coarse gray sandstones of the Scutella breweriana zone rest 

 with a fault contact against the Orindan, which belongs to the Las 

 Trampas Ridge section just to the north. The iipper Monterey is 

 lithologically similar to that seen on the south side of the Mount 

 Diablo anticline and in the vicinity of the town of Walnut Creek. 

 Above the coarse sandstones of the Scutella breweriana zone are about 

 five hundred feet of medium fine, buff to yellow-brown and gray sand- 

 stone in which is found a fauna typical of that in the fine sandstones 

 occupying the same stratigraphic position on San Pablo Bay. Above 

 the fine sandstones of the Monterey comes a series of coarse, massive 

 layers of gray sandstone referable to the San Pablo and similar to the 

 sandstones which characterize the lower San Pablo everywhere in this 

 general region. 



The beds of both the San Pablo and Monterey Groups have prac- 

 tically the same strike and dip throughout and so far as could be 



