48 University of California Publications in Geology [Vol. 7 



Introduction 



Mt. Diablo may be described as the core of an anticline which 

 is overturned and overthrust. The Franciscan series forms the 

 core of the mountain mass. Stratigraphically above this and 

 surrounding the mountain is a series of sedimentary formations, 

 ranging in order through the Knoxville (Jurassic ? to Creta- 

 ceous), Chico (Cretaceous), Martinez (Lower Eocene), Tejon 

 (Upper Eocene) , Monterey (Lower Neocene), San Pablo (Middle 

 Neocene), and Pinole Tuff and Orindan (fresh-water formations 

 belonging to the Upper Neocene). 



The beds described in this paper lie to the north of Mount 

 Diablo. The lowest of the Neocene beds are between six and 

 seven miles north of the main peak. The width of the section 

 described is about two miles, the outcrop, mapped, is about six 

 miles long. The general strike of the beds is about N 70° W; the 

 dip varies from 40° to 20° N E. 



Historical Keview 



The formations of the Mt. Diablo region were first described 

 by Whitney in 1865. 1 In 1891 and again in 1898 Turner 2 

 described the section more in detail, listing thirty-eight species 

 of marine invertebrates from the San Pablo on the north side 

 of the mountain, determined by J. C. Merriam. 



In 1898 J. C. Merriam, 3 in his paper "The Neocene Sea 

 Urchins of Middle California," described the San Pablo forma- 

 tion on San Pablo Bay, and correlated with it marine beds from 

 the vicinity of Mt. Diablo, described as Pliocene by Whitney 

 and Turner. 



In 1909 C. E. Weaver, in his paper on the "Stratigraphy 

 and Palaeontology of the San Pablo formation in Middle Cali- 

 fornia, ' H gave a brief description of the San Pablo in the region 



1 Geological Survey of California, vol. 1, pp. 31, 1865. 



2 Bull. Geol. Soc. Amer., vol. 2, p. 383, 1898; Jour. Geol., vol. 6, pp. 

 443-449, 1898. 



3 Univ. Calif. Publ., Bull. Dept. Geol. vol. 2, no. 4, pp. 109-118, 1898. 



4 Univ. Calif. Publ. Bull. Dept. Geol., vol. 5, no. 16, pp. 243-269, 1909. 



