450 University of California Publications. [Geology 



of it. The edge of these mature hills where they meet the floor 

 of Tehachapi Valley is not a straight line, as is the case with 

 the fault scarp to the west, but is more or less indentate and on 

 the whole sinuous or concave to the north. It is evident from 

 the facts cited that we have here to deal with a quite mature 

 geomorphy which has been entirely unaffected by the disloca- 

 tion upon which the fault block to the west was uplifted. When 

 first viewed from a distance the contrast between these two por- 

 tions of the south boundary of Tehachapi Valley was so striking 

 that the writer supposed that the underlying rocks must be to- 

 tally different. But an inspection of the ground showed that this 

 was not the case. The rocks which underlie the geomorphically 

 mature hills to the east have the same granitic character as those 

 which form the bulk of the fault block mountain to the west with 

 its bold, youthful features. It seems clear, then, that the fault 

 scarp does not extend eastward beyond the dividing line between 

 these two contrasted types of geomorphy. It follows from this 

 that the dividing line between the fault block mountain and the 

 unfaulted, mature hills immediately to the east of it is a trans- 

 verse or north and south fault, and that the fault block is tilted 

 to the west as well as to the south. 



Such a mature geomorphy as has been above indicated is 

 evidently but a remnant of what was once the general condition 

 of the region, and as this mature surface passes down beneath 

 the floor of Tehachapi Valley, it is probable that we have beneath 

 this part of the valley an earlier mature valley of erosion quite 

 different in its configuration from the modern feature. Towards 

 the eastern outlet of Tehachapi Valley, the north and south sides 

 of the valley converge and here the edge of the mature hills is 

 quite abrupt, but their acclivity appears to be that of a stream 

 cliff of a stream no longer functional, whose rocky bed is deeply 

 buried in the alluvium from Cache Creek. 



Western Boundary of Valley. — There remains to be noted 

 the western boundary of the valley. This is a steep mountain 

 slope of very even and but feebly notched front, except for the 

 gap into Brites Valley. This as will appear later is the revet- 

 ment end of a rather narrow fault block and as such has but 

 little water to discharge to Tehachapi Valley and so has been 



