24 CALIFORNIA ACADEMY OF SCIENCES [Proc. 4th Ser. 



the more westerly group. Among its units are included the 

 Temblor, Avenal, San Benito, Panoche, Mount Hamilton, and 

 other ranges of less importance. J. D. Whitney divided the 

 Mount Diablo Range into six sections which he believed to be 

 more or less distinct. For the most part these divisions are 

 offset from each other, having a somewhat en echelon arrange- 

 ment, forming spurs that project in turn into the Great Valley. 

 This fact has been mentioned before, and was first described 

 by the senior author in 1903, in a paper read before the Cor- 

 dilleran Section of the Geological Society of America' though 

 it was not mentioned in the published abstract. The causes 

 and significance of this peculiar and interesting condition have 

 never before been explained, and it is one of the aims of this 

 paper to call attention to it as one of the most important facts 

 to be considered in the study of the diastrophic record of the 

 California Neocene. 



Neocene Deposits. — While the larger portion of the Neocene 

 deposits of California is included in the Temblor Basin there 

 are important areas in the coastal valleys to the south. It is 

 believed that the most complete, and therefore the most rep- 

 resentative, deposits of the California Neocene are to be found 

 within this larger basin. If older Neocene strata exist outside 

 of this area their existence has not been proved, and it appears 

 to be unlikely that any do exist. 



The Mount Diablo Range occupying as it does a central 

 position in this basin should furnish the most reliable key to 

 the physical history, stratigraphy, and classification of the 

 deposits, which are here most representative of the Neocene 

 of California. While Neocene deposits are found in all of the 

 intermontane valleys among the interior ranges, their most 

 complete development is found either within the drainage of 

 the Salinas River, or in some respects, better still, on the east- 

 ern flanks of the Mount Diablo Range, as will be shown here- 

 after. The eastern flank of this range occupies the most cen- 

 tral position of the basin. Descriptions of some of these 

 Neocene strata have already been published in the several 

 papers devoted to difTerent portions of the range,' and in the 



1 Bull. Geol. Soc. Am., Vol. 15, pp. 581 and 582. 



2 Proc. Calif. Acad. Sciences, Vol. II, No. 2; 

 Proc. Calif. Acad. Sciences, Vol. Ill, pp. 1-40; 

 Bull. No. 398, U. S. Geol. Surv., pp. 46-179; 

 Bull. No. 406, U. S Geol. Surv., pp. 31-107. 



