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University of California Publications. [Geology 



is only known as the product of torrential streams emerging from 

 narrow high grade canons upon broad open valleys. Such valleys 

 are geomorphically discordant with the erosional features of the 

 mountains whence the streams emerge, and such discordance can 

 usually only be explained as due to diastrophic movements. This 

 accumulation of coarse alluvium was followed by an outburst 

 of volcanic activity, which gave rise to showers of ashes and 

 scoriae and a flow of andesitic lava. Upon the new surface con- 

 figuration of the region thus established, a lake basin, or possibly 

 several of them, interrupted the normal course of the drainage. 

 In this basin there accumulated the Cable formation consisting 

 of limestones in which fresh water molluscs were entombed, beds 

 of clay, more or less calcareous, and, in the vicinity of incoming 

 streams, beds of gravel and sand. Interstratified with these 

 lacustral beds is an abundance of volcanic tuff also for the most 

 part well stratified. These probably represent the recurrence of 

 volcanic eruptions during the lacustral period, although they 

 may also in large part at least, be explained as the product of 

 the erosion of the surrounding ash mantled country. 



This lacustral condition was brought to a close by another 

 orogenic movement which uplifted the mountains to the north 

 of the valley in which the lake lay. The lake was displaced and 

 its deposits were buried under a vast accumulation of coarse 

 alluvium, the Tehaehapi Formation, evidently the cone of a tor- 

 rential stream actively engaged in the dissection of the new 

 mountain mass. The source of the alluvium was from the north. 



The next event of which we have record is another orogenic 

 movement which deformed the region both by flexure and fault- 

 ing. At this time the pre-Cable volcanics, the Cable Lake beds, 

 and the Tehaehapi alluvium, or at least so much of these forma- 

 tions as are left for our inspection, were together folded in an 

 asymmetric syncline, the most acute deformation occurring on the 

 west side of the trough where the beds are now vertical. At this 

 time the fault scarp which forms the boundary of Tehaehapi 

 Valley on the west was also probably formed. This period of 

 acute deformation was succeeded by a period of vertical stream 

 corrasion till the streams attained their base level and then began 

 to evolve a broad flood plain by lateral corrasion. This flood 



