PHYSIOGRAPHY OF BISHOP CONGLOMERATE 619 



peneplain to the north, burying first the region close to the base of 

 the mountains and later that farther away. In the meantime 

 these more distant parts would be exposed to the agencies of an 

 arid climate until the fans finally reached them. We should expect 

 to find then along this outer zone not a deep residual soil formed 

 during the time of planation, but fresh rock floors resulting from 

 exposure to an arid climate before the fans reached so far out. 



The effect of an arid climate on a monadnock like Aspen Moun- 

 tain should be apparent in the mantling of the slopes with debris. 

 This, owing to the lack of a protective covering of vegetation on 

 the slopes, would be comparatively rapidly carried down by the 

 desert torrents and accumulated at the base as has already been 

 suggested. This is the actual condition at the base of Aspen. 

 Starting at the low area and going toward the mountain one finds 

 that the gravel-deposit is all of local nature and gradually thickens 

 till, near the base of the mountain, it has an observed thickness of 

 over two hundred feet and the base was not seen. It thins again 

 as it laps up on the sides of the mountain. The section radially 

 to the mountain is lenticular in form, the bottom corresponding 

 to the rock-slope of Aspen as developed during the time of plana- 

 tion, and the top being graded to the slope of the desert fans, 

 which is considerably more gentle. 



The bed-rock in the low area is fresh, as already stated; a 

 condition which agrees equally well with the succession of events 

 just postulated, as with the idea of planation under desert con- 

 ditions. 



The relation of the Miller Mountain gravels to the Uintas 

 corresponds in all respects with what we should expect in the case 

 of gravel fans accumulating at the base of high mountains in an 

 arid climate, not only in the nature of the material in the fans, 

 but also in the distribution and general attitude of the deposits. 



Reasoning thus we are led to the conclusion that the period of 

 planation was brought to a close by a renewal of mountain uplift 

 during which the Uintas were greatly elevated with respect to the 

 surrounding plains; that this period of mountain-making was 

 probably followed in this region by a change from a comparatively 

 moist to an arid climate; and that great desert fans of gravel and 



