TERRESTRIAL DEPOSITS OF OWENS VALLEY 745 



fans, down-warping of their surroundings, etc. Such events and 

 resulting processes may be complex. The cause of dissection in 

 this case, however, seems to be the cessation of glaciation, and the 

 process seems simple. 



All the material seen in the bajada, even to the bottoms of the 

 canyons, shows evidence of glacial wear. Before the mountain 

 canyons were glaciated, the fans must have been smaller and lower 

 than now by an amount at least equal to the depths of the canyons. 

 Glaciers were formed, which carved great amounts of material from 

 the heads of the canyons, carried it to their lower ends, and, melting, 

 supplied great quantities of debris-laden waters to flow out over 

 the fan. The fans grew rapidly and became large, out of all pro- 

 portion to those at the foot of the Inyo Mountains, which were 

 not affected by glaciers. 



When the glaciers in the mountains had melted away, these 

 enlarged fans were dissected, for the same reason that a valley 

 train is trenched. The streams now reach the fans with less 

 material than they carried when the glaciers existed, and are able 

 to erode material from the fan. 



The matter may be looked at in another way. The pre-glacial 

 fans, being lower than the present ones, had lower gradients and 

 made a sharper break in gradient at the foot of the mountains, and 

 deposition progressed. Now that the fans are higher, their gradi- 

 ents are steeper, and the break in gradient at the foot of the moun- 

 tains is not so great, and the streams flow out over the fans with their 

 velocities less checked than formerly. This means at least that 

 there will be less deposition on the present fans, and, taken with 

 the fact that the streams have less load, plays a part in the erosion 

 of the fans. 



Presumably the canyons will be deepened almost or quite to 

 the bottom of the glacial material. This depth has nowhere been 

 reached as yet. 



DEPOSITS OF TWO AGES AT THE FOOT OF THE INYO MOUNTAINS 



The older deposit at the foot of the Inyo Mountains is here 

 considered to be a lacustrine deposit, coinciding in age with the 

 lake beds in Waucobi Canyon and those near Haiwee. If this be 



