8 EEPOET UNITED STATES GEOLOGICAL SURVEY. 



to apply them as aids in descriptive geology. These are the Danforth * 

 liiJIs, Gray Hills, Piiion Ridge, &c., the positiou of each of which is 

 shown upon the accompunyiug map. 



DRAINAGE. 



The greater part of the drainage of this district is effected by both 

 the White and Yampa Rivers, in approximately equal proportion, but 

 a large part of the i)ermanent water of both these rivers is derived from 

 the mountain region that lies beyond the district to the eastward. 

 Green River cuts across the northwestern portion of the district, but as 

 it traverses deep caQons in the Uinta Mountains along a part of that 

 portion of its course, it receives very little addition to its waters there 

 at any time of the year except what reaches it by the Yampa. Below 

 the caiions, however, a few minor drainages reach Green River from 

 the east side; and Ashley's and Brush Creeks empty into it from the 

 west side. 



The water-shed which divides the drainage between the White and 

 Yampa Rivers consists of an irregular and somewhat tortuous line of 

 hills, generally recognizable as a water-shed crest when seen from other 

 elevations at a distance. The eastern part of this water-shed lies along 

 the crest of the Danforth Hills, and is deflected so that it has there an 

 almost due southeast and northwest trend, the eastern end of the dis- 

 trict being almost wholly drained into the Yampa. The western portion 

 of the water shed, comprising the greater part of its length, has an ap- 

 proximately due east and west course. Its western terminus is upon 

 the western end of Yampa Plateau, a large, broad mountain mass, which, 

 as already explained, lies adjoining and is accessory to the great Uinta 

 Uplift. The course of the water-shed upon the plateau is in some places 

 within four or five miles of the Yampa River, which in this part of its 

 course runs in a deep, narrow canon. The relation of these drainage- 

 lines and their water-sheds to the displacements of the strata in this_ re- 

 gion will be discussed under appropriate heads upon subsequent pages. 



That portion of this district which lies between the two great moun- 

 tain systems before named is more or less deeply cut by drainage-chan- 

 nels, leaving be-tween them many elevations that are quite worthy of 

 the name of mountains. The region embracing this district lies far 

 within the limits of that great portion of the United States domain in 

 which the annual rain-fall is insufficient for the purposes of agriculture. 

 In consequence of this dryness of the climate, the drain age- valleys and 

 ravines just referred to, which lead into the rivers, are with few excep- 

 tions dry during a great part of the year. These drainage-channels, 

 which for convenience of description are called " dry drainage chan- 

 nels," all show marks of an abundant and strong flow of water and of 

 great and rapid denudation of the surface that is drained by them dur- 

 ing the wet season of the year. A stranger, not familiar with the meteor- 

 ological conditions prevailing in this region, travelling through it in 

 the summer, would be impressed with the belief that the country was 

 formerly a well-watered one, a land of a multitude of flowing streams 

 which, for some cause not now apparent, had suddenly and permanently 

 ceased to flow, and that in consequence the land had recently changed 

 to a dry and barren one. 



The ])resent surface features of the district are almost wholly due to 

 ;two principal causes, namely, elevation and consequent flexion and 



*So named iu honor of Rev. E. H. Danforth, Indian agent at the White Eiver 

 agency. 



