APPARENT CONFORMITY OF CENOZOIC AND MESOZOIC. 399 



Pliocene, are everywhere apparently conformable. about Mount Diablo, and 

 the series probably rests unconformably on the Knoxville shales and meta- 

 morphic rocks. Positive evidence of this non-conformity was, however, 

 difficult to obtain, though the occurrence of metamorphic pebbles in the 

 Chico and later terranes and the excellent evidence, both here and elsewhere, 

 as to the highly metamorphic rocks being entirely of Neocomian (Knoxville) 

 age makes this practically certain. 



Post-Pliocene Beds. — The post-Pliocene deposits consist mostly of loose 

 beds of sand and gravel. In the gravel are fragments and pebbles of red 

 phthanite and other metamorphic rocks, of Pliocene shale, and of fossilif- 

 erous sandstone of probably Miocene age. 



South of the mountain these beds are disturbed in one place, about a mile 

 south of Wall point, where they dip southward at an angle of 45°. Ac- 

 cording to Professor Whitney,^ the post-Pliocene beds north of the Pliocene 

 at Kirker pass conformably overlie the Pliocene and dip toward the north. 



The Epoch of Upheaval. 



The main upheaval of the Coast ranges occurred in post-Miocene times. 

 This was the result of a lateral stress that formed ranges having a north west- 

 and-southeast trend. The stress may have operated in the vicinity of Mount 

 Diablo, forming, perhaps, a low ridge ; but there is evidence that the main 

 upheaval of the mountain occurred at the close of the Pliocene. From an 

 examination of the geological map (plate 15) and the sections (figures 1, 2, 

 and 3), it is plain that in the main the strata were thrown into their present 

 positions by the elevation of the central metamorphic mass. 



In a general way the strata north of the main peak dip northward, and 

 those to the south of the main peak dip southward. The uplift was so vig- 

 orous that part of the strata to the south were actually reversed in position, 

 and in places now dip northward at a high angle, the older strata overlying 

 the younger. This reversal is greater at some points than at others. It is 

 particularly observable west of Cave point and east of Tasajero creek. At 

 the latter locality there is also a very evident fault, the horizontal throw 

 of the strata being about one mile. This displacement is a conspicuous 

 feature on the map forming plate 15. 



The Pliocene rocks exposed by the Railroad ranch reservoir partake in 

 this reversal, and it is likely that this is also the case with the Pliocene at 

 Tasajero creek. 



The strata immediately surrounding the metamorphic mass are, except 

 for a space on the southwest, of Cretaceous age. Next to the Cretaceous, 

 going away from the mountain in any direction, are Eocene (Tejon) strata ; 



* Geology of California, vol. I, 18(i5, p. 32. 

 LIX— Bull. Geol. Soc. Am., Vol. 2, 1890. 



