Vol. 4] 



Lawson. — Tehachapi Valley System. 



447 



north of the present Tehachapi Valley, these materials having 

 been brought to the seat of deposition by a high grade stream 

 engaged in the rapid dissection of a recently uplifted mountain 

 block. It has been shown further that the later orogenic move- 

 ment which deformed the Tehachapi Alluvium was characterized 

 by a recurrence of the uplift on the north side of the present 

 Tehachapi Valley. The stream which gave rise to the Tehachapi 

 Alluvium would, by this second uplift, have had the grade, to 

 which it had attained, again accentuated. This accentuation of 

 grade would apply now to the country occupied by the alluvial 

 cone and the latter would consequently be dissected. The dissec- 

 tion of the cone woiud continue till a grade profile was estab- 

 lished, when the stream would begin to meander and evolve an 

 ever-widening flood-plain on a stream-cut terrace. This terrace 

 would be cut out of the alluvium and the rocks adjacent to it 

 or under it indifferently. The history thus sketched appears to 

 be that of the broad stream terrace which has been described as 

 traversing the Tehachapi Alluvium, the Cable lake beds, and the 

 various rocks of the Bed-rock Complex above Cable. 



If this interpretation be correct, then it is clear that the 

 drainage, at the time that the terrace was functional as a flood- 

 plain, was from the north and not towards the north as at 

 present. 



Dissection and Reversal of Drainage. — Since its completion 

 the terrace has been deeply dissected and this dissection has been 

 effected by a northerly flowing stream, the present Tehachapi 

 Creek which drains into the Great Valley. In the vicinity of 

 Cable this dissection amounts to 350 feet or more ; and in the 

 tributary creek, which comes in from the left from China Hill, 

 and which joins Tehachapi Creek about half a mile above Cable, 

 cutting through granite, schist, limestone, Cable lake beds and 

 Tehachapi Alluvium, the dissection is about 250 feet in depth. 

 The valley of this stream where it cuts through the hard rocks 

 has a width of about 150 feet and in the soft rocks of over 

 300 feet on its bottom. 



Two circumstances seem to have conspired to bring about 

 the reversal of the drainage above indicated. It has been shown 

 that the terrace surface slopes to the south and passes beneath 



