TERRESTRIAL DEPOSITS OF OWENS VALLEY 739 



Decrease in volume and consequent decrease in velocity took 

 place on the plains for another reason also. It rained heavily 

 or snow melted rapidly in the mountains, and the mountain streams 

 acquired great volume and velocity. When the rain ceased, or 

 the temperature dropped below 32 , the flood on the plains sub- 

 sided from lack of supply from above. This undoubtedly furnished 

 conditions under which a large proportion of the material of the 

 fans was deposited. 



Glaciation has played a large part in the deposition of the Sierra 

 bajada. Glaciers prepared immense amounts of material in the 

 mountain canyons for transportation by streams. At the same 

 time they furnished great volumes of water to act as the transport- 

 ing agent during the melting-season. The initial volume and 

 the load being at a maximum, deposition took place on the plains at 

 an unusually rapid rate and to an unusually great extent. 



FORMS TAKEN BY THE DEPOSITS 



Deposition necessarily took place at the foot of the mountains, 

 at the end of the mountain canyons. The streams flowed on down 

 over the deposit it had made, until it disappeared; hence the fans 

 slope away from the mountains. While the stream was depositing 

 and especially at times when floods were subsiding, channels were 

 rilled, distribution took place, new channels were made and filled, 

 and water courses changed constantly. In each new distribution 

 the channels diverged from the mountains. The resulting feature 

 is broader near its edge than near the head; that is, it is roughly 

 fan shaped. 



In the Inyo Mountains there is little precipitation, the canyons 

 are far apart and small, and the fans are accordingly too far apart 

 and have grown laterally too short a distance to have been joined. 

 The result is a series of separate fans. In the Sierras, the streams 

 issue at sufficiently small intervals and have built fans of sufficient 

 size, so that they have coalesced to make a compound fan, pied- 

 mont alluvial plain, or bajada. 



When fans first join, the compound fan is a series of fans, with 

 low places between. If Oak Creek, Shepard Creek, and Hogback 

 Creek are considered as types, there is a tendency for streams to 



