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University of California Publications. [Geology 



the modern alluvium of Tehachapi Valley, or, more particularly, 

 beneath the alluvium of the China Hill cone. What its extent 

 may be beneath this alluvium is unknown but it is clear that 

 the accumulation of this alluvium upon the southern extension 

 of the flood-plain would tend to pound back the waters coming 

 from the north and cause them to seek another outlet if such 

 were available. 



Such an outlet was provided by the headwater erosion of a 

 stream on the Great Valley side of the mountains. The two 

 orogenic movements which have been recorded as affecting the 

 mountains in this direction greatly accentuated the grade of the 

 streams on the north side of the divide, and one of these, the 

 present Tehachapi Creek, caused the divide to migrate southerly 

 till it reached the terrace of the southerly flowing stream, and 

 not only effected its capture but provided an outlet for its 

 beheaded portion, the waters of which, in greatly diminished 

 volume, were obstructed by the excessive accumulation of allu- 

 vium upon its flood-plain. The question now arises as to the 

 cause of this excessive accumulation of alluvium. The answer 

 to this question is very pointedly suggested by a consideration 

 of the geomorphic features of the region which is the source 

 of that alluvium. The alluvium all comes from a few sharp, 

 torrential canons which emerge, above grade, upon Tehachapi 

 Valley, from the straight, bold wall of Tehachapi mountain 

 which forms the western half of the southern boundary of the 

 valley. The geomorphic discordance which these canons present 

 to the broad, alluviated Tehachapi Valley is in itself ample 

 proof of the fact that the mountain mass which they dissect is 

 a fault block. The northern slope of the mountain is steep and 

 on the whole not greatly degraded. This face has a regular east 

 and west trend, transverse to the strike of the schists and lime- 

 stones which together with granitic rocks make up its mass. The 

 canons which discharge the alluvium are relatively so insignifi- 

 cant that they do not greatly notch the longitudinal profile of 

 the mountain and their mouths can scarcely be perceived at a 

 distance of a few miles. If such evidence that the face of the 

 mountain is a degraded fault scarp were not sufficient, more 

 direct evidence may be observed at the point where Antelope 



