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University of California Publications. [Geology 



ley were established. It must, therefore, antedate the modern 

 Tehaehapi Valley, i.e., it must antedate the fault block which 

 forms the south boundary of the western half of the valley. This 

 being' so the gorge must have been coexistent with the stream 

 which evolved the broad terrace at the west end of the valley, 

 and if this be conceded then the gorge was that of a small eastern 

 affluent of the larger stream. From this line of reasoning we 

 thus reach the conclusion that the drainage of this outlet was 

 also at one time toward the area of the present Tehaehapi Valley 

 and that this drainage has been reversed. The causes of the 

 reversal are doubtless two-fold. The uplift which terminated 

 the process of flood plain expansion in this region was without 

 doubt effected by a movement on the great fault which bounds 

 the Sierra Nevada on the east and southeast and which here 

 separates them from the Mohave desert. Such a movement 

 would have beheaded this gorge and have rendered it an easy 

 matter for the rapidly accumulating alluvium in the now moun- 

 tain-girt Tehaehapi Valley to congest the gorge and cause the 

 waters to flow out to Mohave. 



It thus appears that both of the outlets of Tehaehapi Valley 

 antedate the valley as we know it to-day, and that they are both 

 cases of reversed drainage brought about by orogenic move- 

 ments, inducing stream capture and the obstruction of the 

 beheaded streams by great alluvial cones. 



BRITES VALLEY. 



Brites Valley opens into Tehaehapi Valley at the southwest 

 corner of the latter through a gap between the fault scarp which 

 bounds both valleys on the south and the northeast corner of 

 Bear Mountain. The trend of the valley is northwest and south- 

 east, in which direction it has an extent of miles. Its breadth 

 is about li miles. Its southern boundary is the western exten- 

 sion of the same degraded fault scarp as that which bounds 

 Tehaehapi on the south. Its northeastern boundary is a moun- 

 tain wall with a very straight trend and a steep, even, little 

 notched slope, which can only be interpreted as a fault scarp, 

 The bearing of this scarp is northwest and southeast, thus mak- 

 ing an angle of about 45° with the strike of the rocks. It may 



