402 



University of California Publications. 



[Geology 



which resulted in faulting along the face of Breckenbridge 

 Mountain found its expression in arching in the Greenhorn 

 Mountains. Now the Greenhorn Mountains lie to the west of 

 Hot Springs Valley and any deformation such as is here sug- 

 gested would have the tendency to pond back the Kern. That 

 tendency would, however, be effective only if the corrasive action 

 of the Kern failed to keep pace with rate of uplift. But for 

 several miles below the region of aggradation, and still on the 

 east side of the uplift, the Kern is flowing in a rocky trench and 

 it would thus appear that the Kern had been fully able to keep 

 pace in its rate of down-cutting with the rising arch in its path. 

 We cannot, therefore, adduce this special phase of the deforma- 

 tion of the region as the cause of the aggradation of the Kern 

 and the South Fork above their confluence ; and even if such a 

 cause were admitted, it would offer no explanation of the dual 

 character of Hot Springs Valley. No amount of simple aggrada- 

 tion due to the ponding of the Kern would account for the 

 notched median ridge between the two portions of the valley. A 

 more fruitful hypothesis is suggested by the notches in this ridge. 

 They have the character of very short residual trunks of 

 beheaded stream valleys. If such be their origin, then the valleys 

 or canons of which they once formed a part could only have 

 been beheaded by a fault along the east side of the median ridge, 

 with a downthrow to the east. The straight and quite precipi- 

 tous east side of the median ridge becomes under this hypothesis 

 a degraded fault-scarp, the notches in which are antecedent to 

 the existence of the ridge. Does this hypothesis afford an ade- 

 quate explanation of the two classes of phenomena with which 

 we are here concerned ? Seemingly it does. By the development 

 of a fault along what is now the east side of the median ridge 

 with a downthrow to the east, a trough would be formed, the 

 aggradation of which would give us the flat bottomed eastern 

 moiety of Hot Springs Valley. If the fault-scarp were rather 

 rapidly formed, as it probably was, the waters of the Kern would 

 be impounded against it and a process of aggradation inaugur- 

 ated. The impounded waters would rise to the level of the lowest 

 notch in the face of the fault-scarp, which would probably be 

 the trench of the Kern itself, and so resume their former channel 



