214 SOUTHERN CALIFORNIA GEOLOGY 



RELATIONS OF THE PHYSIOGRAPHY TO 

 FAULTING AND SEISMICITY 



Inasmuch as the rehef of the master highlands and 

 lowlands is largely the result of the master faulting, 

 their histories, together with the subordinate condi- 

 tions of seismicity, must be somewhat inter-related. 

 The fact that the relief features have moved up and 

 down or laterally by successive impulses in harmony 

 with the fault movements is well shown in the in- 

 stances of the San Bernardino Plateau, the body of 

 which is a segment of a former, diversified, lowland 

 peneplain which has been elevated by several uplift 

 stages to its present position. Correspondingly there 

 have been developed on its sides a broad series of step- 

 down faults and bench-like terraces and its summit 

 area shows evidence of several, interrupted erosion 

 cycles. These conditions all serve as records of 

 Pleistocene and perhaps earlier history. The youngest 

 highlands, on the other hand, of which the Dominguez 

 Range is an example, are of low altitude and exhibit 

 but few evidences of the marginal phenomena above 

 mentioned. 



Likewise we may deduce the fact that in Southern 

 California the structural highlands of greatest alti- 

 tudes are relatively the older ones and that those of 

 lower altitudes are the younger in age. These condi- 

 tions are quite different from those usually observed 

 in other and older regions of the United States, where 

 the lower mountains are the older, having been worn 

 down by long erosion, while the higher mountains 

 are the newer. 



'See "Geology of the San Bernardino Mountains" by Francis VauKhan. 

 Univ. Cal., Geol. Bull., 1922. 



