12 EEPOET UNITED STATES GEOLOGICAL SUEVEY. 



is the scattered drift so common in a large part of this region. It 

 reaches considerable thickness upon the higher surface of the basin, and 

 also constitutes a large j)roportion of the bulk of the water-shed ridge 

 before referred to. Yam pa Eiver traverses this part of the basin from 

 east to west, and it might, therefore, with some propriety, be designated 

 as a large park. But its basin-like character constitutes a greater and 

 more conspicuous feature than any of the other similar excavations in 

 the vicinity, especially as it occupies the lowest ground between the 

 eastern end of the Uinta chain and the mountains that lie to the east- 

 ward of this district. Other features of both portions of Axial Basin 

 will be referred to in the description of the valley of Yampa Eiver. 



Bed Boeli Basin. — This basin is located adjacent to the northwestern 

 portion of Yampa Plateau, and near the confluence of Yampa Eiver 

 with the Green. Midland and Axial Basins have been eroded out of 

 soft strata that rest upon comparatively gentle anticlinal axes; and 

 Coyote Basin has been excavated by erosion out of other soft strata 

 that rest in an equally gentle synclinal. But Eed Eock Basin differs 

 materially from those in the character and condition of its foundation, 

 for it really consists of a very deep synclinal flexure of the hard strata 

 of Carboniferous age, from which the somewhat softer, but comparatively 

 firm Triassic strata have been removed by denudation, except at the 

 bottom of the flexure, which is the bottom of the basin, where Triassic 

 strata still remain. It is the southern side of this great synclinal that 

 I have called the Yampa Flexure, and which synclinal separates the main 

 Uinta, from the Plateau Uplift. This great synclinal flexure reaches its 

 maximum depth at the w^est end of Eed Eock Basin, where it ends 

 abruptly against a mountain mass that projects northwardly from Yampa 

 Plateau, by a north and soutj^ fault of about 2,000 feet downthrow; the 

 depth of the basin below the northern border of Yampa Plateau being 

 also about 2,000 feet. From this fault, the basin proper extends east- 

 ward five or six miles, when it becomes immediately narrower and grad- 

 ually shallower, and thence extends eastward as a long narrow syncli- 

 nal valley until it is lost among the hills at the eastern end of the Pla- 

 teau Uplift. This valley and the deep basin with which it is continuous 

 would seem to be a much more natural place for Yampa Eiver to flow in 

 than the one it has chosen, and which will be presently described, if it 

 were not for the theory already explained that the streams are older than 

 the flexures of the strata. The breadth of Eed Eock Basin is about the 

 same as its length. Its depth is so great that from the southern brim, 

 the bottom looks comparatively plain, but it is really traversed by deep 

 gorges that are cut in the red Triassic strata there, between which- 

 gorges the surface is rough and hilly. 



r 



VALLEYS 



The descriptions immediately following are of the river — valleys as 

 surface features. Their relations to the displacements of the strata over 

 which the rivers flow will be discussed in a subsequent chapter. The 

 parks being only portions of the valleys, the description of each of these 

 will be included with that of the valley to which it belongs. 



White Eiver Valley. — White Eiver, which in summer is a rapid 

 stream of clear, cold water, rises by numerous small branches among the 

 gorges and ravines of White Eiver Plateau, all of which have their conflu- 

 ence with the main stream before it enters this district on its w^estward 

 course. The'bed of the river is almost everywhere strewn with drift- 

 pebbles, and its banks are usually easy of approach, except where they 



