Vol. 4] 



Lawson. — Tehachapi Valley System. 



443 



alluvium. These clays are probably a portion of the fresh-water 

 formation and if so, they indicate a northerly dip of the forma- 

 tion. 



It thus appears that the Cable fresh-water beds lie in an 

 asymmetric synclinal trough, the nose of which is situated below 

 Cable at the point where the strike changes its course from 

 northwest and southeast to north and south. An interesting 

 fact indicating at once the former extent of the lake beds and 

 the nature of the deformation to which they have been subjected 

 is the occurrence, on a spur of the mountains to the north of 

 Tehachapi, at a point about 2 miles north of the station, of an 

 outlying patch of cherts plastered as it were on the face of the 

 mountain slope, the dip of the beds determining the angle of 

 declivity. The projection of these beds to the northeast would 

 carry them over the entire southerly slope of the mountains on 

 this side of the valley. 



Tehachapi Formation. — In the trough above indicated lies a 

 great body of coarse alluvium, the Tehachapi Formation, repos- 

 ing upon the Cable fresh-water beds and having approximately 

 the same areal distribution as those beds. It is well exposed in 

 many steep slopes and railway cuttings in the canon of Tehachapi 

 Creek above Cable. In these exposures it is seen to be composed 

 of a coarse aggregation of rock fragments such as is usually 

 found near the apex of the alluvial cone of a steep-grade stream. 

 These rock fragments are in a fresh undecomposed condition 

 and are but slightly cemented together so that separate blocks 

 may be detached from the aggregate with ease. These materials 

 comprise, not only granite rocks, schists, limestone and quartz 

 of the Bed-rock Complex, but in certain portions of it there are 

 numerous blocks of the Tank Andesite. In the lower part of 

 the formation where it rests upon the uppermost beds of the 

 Cable formation, the rock fragments are comparatively small, 

 masses the size of a fist and less predominating and there is a 

 considerable admixture of sand. Here the material is rudely 

 stratified and where the contact is exposed in the railway cuts 

 above Cable the dip of this stratification is the same as that of 

 the underlying lake beds, about 12° to the southwest. In the 

 higher parts of the formation the angular blocks of which it is 



