IjAWSON.] 



The Upper Kern Basin. 



365 



the Summit Upland, sessile upon the butt of the wedge, was lifted 

 into a zone of more vigorous erosion. 



Prior to this uplift, however, volcanic vents opened in some 

 of the high valleys and veneered their floors with sheets of 

 basalt. The best example of this, and, indeed, the only exam- 

 ple, although others will doubtless be found, is the lava which 

 lies upon the surface of the Little Kern Plateau and which has 

 been subjected to the same dissection as the plateau itself. Into 

 this uplifted mass the streams of the region sank their trenches 

 and, on reaching a grade adjusted to their load, began to mean- 

 der and widen these trenches into valleys. In this way, with 

 the cooperation of atmospheric erosion, the present High Valleys 

 of the region, Chagoopa Plateau, Toowa Valley, and the Little 

 Kern Plateau were evolved. The time necessary for the evolu- 

 tion of these High Valleys occupied the greater part of the 

 Quaternary. Not only were the High Valleys evolved as broad, 

 flat, or very gently sloping, plains in the midst of the mountains, 

 but the mountains themselves surrounding these valleys were 

 reduced to mature slopes. The second and greater uplift then 

 occurred. This initiated the down cutting of the present canon 

 system of the Sierra Nevada, of which Kern Canon is one of the 

 finest examples. But Kern Canon is evidently controlled by some 

 structural feature, which was probably established at the time 

 of this second uplift. This structure appears not to have been 

 of the nature of a fault of sufficient throw to appreciably dislo- 

 cate the High Valley floors. It is, therefore, suggested that it 

 was of the nature of a rift fissure. This hypothesis, on critical 

 examination, is found to be in harmony with many features of 

 the canon, particularly with the evidence of inslipping of slabs 

 and wedges of the canon walls after the canon had attained 

 approximately its present form. This inslipping is probably due 

 to a renewal of the opening of the original rift fissure in later 

 time. The inslipping has had the effect of materially widening 

 the canon; but certain portions of the inslipped masses have 

 failed to slip as far as others, and they now constitute the 

 peculiar buttresses of the canon walls, particularly the west wall, 

 which appear to be a new type of geomorphic form signalized by 

 their designation as kembuts, the troughs which separate these 



