Mount Diablo 



157 



three areas: (a) The metamorphic sedimentary complex, about 

 ten square miles, includes the main Mt. Diablo Peak and North 

 Peak. Here are found all the forms of metamorphic sedi- 

 mentary rocks that occur in the San Francisco Bay region. 



ANTIOCH 



MT DIABLO QUADRANGL 



FIG. 50. Structural map of Mount Diablo, showing upthrust mass of 

 Franciscan rocks through Upper Jurassic and Cretaceous formations. J, Fran- 

 ciscan; K, Upper Jurassic and Cretaceous; T. Tertiary. Beginning in late 

 Jurassic time and ending at the close of the Cretaceous there were five epochs 

 of subsidence and sedimentation throughout the Mount Diablo area. (J. A. 

 Taff.) 



(b) Massive diabase and basalt, igneous rocks, occupy about five 

 square miles in the northwestern part of the mountain. In- 

 cluded in this area are Mount Zion, Black Point, and Eagle 

 Point, (c) Metamorphic igneous rocks extend diagonally 

 across the mountain as a large intrusive mass between the meta- 



