Vol. 5] 



Weaver. — San Pablo Formation. 



249 



studies of the materials in the two formations it is evident that 

 they are quite intimately related. Taken as a whole, he con- 

 siders the Purisima fauna as younger than the aggregate San 

 Pablo fauna. He concludes that the greater part of the San 

 Pablo should without question be placed in the Miocene while the 

 major portion of the Purisima is undoubtedly Pliocene. 



GEOGRAPHIC DISTRIBUTION, is 



The San Pablo formation is widely distributed in the Coast 

 Ranges of California. To the north of San Francisco Bay it 

 occurs as a long narrow belt lying on the eastern flank of the 

 Blue Ridge and extending in a northwesterly-southeasterly direc- 

 tion from the town of Vacaville to Lake County. The belt 

 averages about four miles in width and perhaps thirty in length. 

 A second occurrence lies in the hills between the towns of Napa 

 and Sonoma. Here it outcrops in the eastern bluff of Carneros 

 Ridge and along the valley of Carneros Creek. It occupies a 

 belt about one mile in width and six miles in length. 



The type locality where it has been most thoroughly studied 

 occurs in Contra Costa County in the vicinity of San Pablo Bay. 

 Here it occupies a V-shaped belt extending in a synclinal fold 

 from El Cierbo on the north in a southeasterly direction to near 

 the head of Franklin Canon, where it turns and swings around 

 to the southwest and emerges on San Pablo Bay about one mile 

 south of the town of Rodeo. This is one of the best known occur- 

 rences of the San Pablo in middle California. 



Farther east this formation is again well represented in the 

 district north and south of Mount Diablo. It occurs as a broad 

 belt extending in a northwest to southeast direction on the north- 

 ern flank of Mount Diablo. This belt lies near the foothills of 

 the mountain and outcrops prominently in the hills on either 

 side of Kirker's Pass and Markeley Canon and extends from 

 there to Karquinez Strait. On the south side of the mountain 



is In the compilation of the statement of geographic distribution and 

 stratigraphic relationships of the San Pablo, the manuscript geological maps 

 of the Concord, San Francisco, Mt. Diablo, and Napa quadrangles prepared 

 for the U. S. Geological Survey from the field studies of Andrew C. Lawson, 

 John C. Merriam, G. D. Louderback and C. E. Weaver have been freely used, 

 and many of the facts here stated in print for the first time are clearly set 

 forth in these maps. 



