NORTH OF MOUNT DIABLO 



285 



from 15 to 40 degrees. The greatest width of these outcrops is about 

 two and a half miles. 



The beds of the Meganos Group in this area rest unconformably on 

 those of the Martinez Group. This unconformity, as stated above, was 

 first described by E. E. Dickerson. The Lower Tejon, as recognized at 

 that time, is the base of the Meganos, as described in this paper. The 

 Meganos beds in this area have a maximum thickness of approximately 



V//// 



r/////// 

 'w///////\ 



Figure 1. — Cross-section sJioiving the Eocene Groups as found on the north side of 



Mount Diablo 



Kc = Chico. Tmt = Martinez. Tst = Meganos. Ttj = Tejon. Tmk = Markley 

 (Oligocene). 



3,000 feet. The section may be roughtly divided into five lithologic mem- 

 bers; these, beginning at the base, will be designated divisions A, B, C, 

 D, E.- 



Summary of lithology of section.— The following is a generalized sec- 

 tion of the Eocene groups as found on the north side of Mount Diablo. 

 The Martinez portion of the section is copied from Dickerson's paper,^ 

 "Fauna of the Martinez Eocene, California." 



Feet 

 6. Clay shales with minor amount of sandstone. . 500 

 5. Fine, buff-colored sandstone ; in places hard, 



calcareous layers contain marine fossils 175 



4, Sandy shales ; exposures poor ; soil very red ... 75 



3. Light gray to white, angular-grained sand- 

 stones, coarse to medium in texture ; cross- 

 bedding common, with minor layers of choco- 

 late-colored shales ; two important coal 



layers 75-400 



2. Chocolate-colored shales, ashy in places, with 

 thin lenticular layers of coarse sandstone ; 

 coal layer locally known as Black Diamond 



vein 50 



1. Conglomerate 0-20 



Unconformity . 



Tejon Group . 



1 R. E. Dickerson : Univ. of California Publ. Bull. Dept. Geol.. vol. 8. no. 6. 1914, p. 71. 



