34 



CRANDALL— SAN FRANCISCO PENINSULA. 



[January 4, 



plainly in two places, near Ocean View and on the bay shore north 

 of San Bruno Point. 



San Andreas-Portola Fault. — The most important fault line on 

 the San Francisco Peninsula is the San Andreas Portola fault. It 

 is plainly discernible in the bluffs at Mussel Rock, and from there 

 it runs toward the southeast through San Andreas and Crystal 

 Springs Lakes. This same fault continues to the southeast through 

 the Santa Cruz quadrangle, where it is known as the Portola fault. 

 This is one of the main lines of weakness in the Santa Cruz moun- 

 tains, and it has been the line of movement at various times. There 

 have been at least two important movements along this fault line, 



Fig. 12. 



A partial view of the anticline at San Bruno Point showing the sandstone 

 and shale beds dipping northeast. 



for the Franciscan sandstone lying northeast of the line is geolog- 

 ically higher than that on its southwest side. Since the movement 

 that caused this dislocation of the Franciscan rocks there was 

 another movement after the deposition of the Merced series which 

 resulted in the tipping of the Merced beds toward the northeast. 

 The steepness of the dip of these rocks increases from Lake Merced 

 southward to Mussel Rock. This second movement brought the 

 Franciscan beds on the northeast side into a position but slightly 



