1922] Vaughan: Geology of San Bernardino Mountains 399 



south fault through Fry Mountain by which the basalt cap has been 

 broken, so that it is possible that all of this minor faulting was effected 

 at an earlier period than the uplift of the old surface on Fry Mountain. 



The most interesting fault in this region is the San Andreas, since 

 it has been the locus of many movements resulting in severe earth- 

 quakes, notably those of 1857 and 1906. 2:! About twenty miles west 

 of this quadrangle the fault cuts diagonally between the San Gabriel 

 and San Bernardino ranges and then skirts the south side of the latter, 

 as is evidenced by the steep wall which the mountain mass presents 



N S 



Fig. 10. Overthrust on the east side of Stubby Canon at its mouth. 



to the San Bernardino Valley. The physiographic expression (see 

 map) can be readily followed along Potato Canon to Oak Glen and 

 thence a mile east of Pine Bench. Here the trace of the fault is lost 

 from sight for nearly two miles, but is again seen on the north side 

 of the valley at the head of Hathaway and Potrero canons and along 

 the "West Branch of Millard Canon. 



Crossing Millard Canon, it is again lost until about two miles west 

 of Stubby Canon, where definite displacement can be seen. Here the 

 Hathaway sediments abut upon the schists with a nearly vertical con- 

 tact ; but just west of Stubby Canon the dip of the fault plane is 70° 

 to the north, so that the schists on the north override the fanglomerates 

 oh the south. Since the schists are the older, it is apparent that the 

 fault is a thrust. On the east side of the canon a block of gneiss on 

 the south has been faulted up against Cabezon fanglomerate resting 

 on gneiss on the north. From Stubby Canon eastward to Cottonwood 

 Caiion the position of the San Andreas fault cannot be exactly deter- 

 mined. Only in a few places can the more recent sediments be seen 



- 3 Eeport of the State Earthquake Investigation Commission upon the Cali- 

 fornia earthquake of April 18, 1906, Carnegie Institution of Washington, D. C, 

 1908. 



