248 



University of California Publications. 



[Geology 



of Tomales Bay. Marine fossils were found in the beds and he 

 considers them to be of San Pablo age. Similar beds were ob- 

 served at Pleasant 's and Capay Valleys, and these are also con- 

 sidered as San Pablo. 



In 1905 Mr. F. M. Anderson, 13 in a stratigraphie study of the 

 Mount Diablo Range of California, divides the later Neocene 

 beds into the Coalinga and the Etchegoin beds. The former he 

 considers to be the equivalent of the uppermost Contra Costa 

 County Miocene and the Etchegoin beds as the equivalent of the 

 San Pablo beds. He considers the San Pablo beds at San Pablo 

 Bay and Kirker's Pass to represent only the lower portion of the 

 Etchegoin beds or rather the Etchegoin sands. They rest un- 

 conformably upon the Coalinga beds. He considers them as 

 probably of Pliocene age. 



In 1906 Dr. Ralph Arnold, 14 in his paper on the Tertiary and 

 Quaternary Pectens of California, gives an extended account of 

 the San Pablo areas in various parts of the state. He states : 

 "the formation at the type locality consists of a series of sand- 

 stones, tuffs and ashes with an approximate total thickness of 

 between fifteen hundred and two thousand feet. At this locality 

 it rests apparently conformably upon the Contra Costa County 

 Miocene. In the Salinas Valley and at many other places for- 

 mations which are probably the ecpiivalent of the San Pablo rest 

 unconformably upon the Monterey shale. In the Santa Cruz 

 quadrangle beds containing the supposedly characteristic San 

 Pablo echinoderm Astrodapsis tumidus Remond, rest uncon- 

 formably upon the Monterey and are overlain conformably by 

 at least a part of the Purisima (Lower Pliocene)." Lists of 

 fossils are given from the San Pablo at the type localities and 

 from the Santa Margarita formation in the Salinas Valley, which 

 he considers as probably the equivalent of the San Pablo. He 

 describes the Purisima formation as consisting of a series of 

 conglomerates, fine-grained sandstones, and sandy shales having 

 a total thickness of about eight hundred feet and being typically 

 developed in the vicinity of the lower portion of Purisima Creek, 

 San Mateo County. He shows that from field and laboratory 



13 Proc. Calif. Acad. Sei. Geology, vol. 2, no. 2, p. 174. 

 !■* U. S. Geological Survey. Professional paper 47, p. 22. 



