WHITE.] SURFACE FEATURES PARKS AND BASINS. 11 



ous drainage-channels, some of which are quite large ; but even these 

 are nearly or quite without water in summer. The synclinal within 

 which this basin lies is partially surrounded by the great bend of the 

 Midland Flexure which is represented on the geological map, and is also 

 described in a following portion of this report. 



Axial Basin. — This basin occupies a great anticlinal axis, which is 

 the eastward prolongation of the vanishing axial flexure of the Uinta 

 Mountain uplift. It is so long and narrow that the term " basin " does not 

 apply to it with strict accuracy, but the use of such a term in this con- 

 nection is not likely to be misunderstood. It extends from Junction 

 Mountain nearly to the eastern border of the district, and is divided 

 into two portions by Yampa Mountain, which is a sharp upthrust of 

 Paleozoic rocks. Junction Mountain is a precisely similar upthrust of 

 Paleozoic rocks, and it also occupies a similar position upon the TJinta 

 axis, at the west end of the basin. Indeed it separates that portion of 

 the basin which has been called Lily's Park from the main portion, in 

 the same manner as, but less completely than, Yampa Mountain has 

 divided that basin into two parts further to the eastward. 



The boundaries of the eastern portion of the basin, that which lies 

 east of Y^ampa Mountain, are more clearly definable than those of the 

 western portion are, because they consist mostly of escarpment bluffs. 

 This eastern portion of Axial Basin is bounded on the west by Yampa 

 Mountain ; on both the north and the south sides by escarpments of 

 Fox Hills strata, and it ends eastwardly by a gradual rise of the whole 

 land to the White Eiver Plateau. The whole of this eastern portion of 

 the basin was primarily eroded out of the shales of the Colorado Group, 

 but for a distance of about four miles east of Yampa Mountain the sur- 

 face is covered by the friable strata of the Uinta Group. Upon the top of a 

 hill aboutthree miles east of the eastern border of this depositof the Uinta 

 Group rest some of the strata of the base of the Fox Hills Group, but 

 with these exceptions all the surface of the basin is occupied by the 

 shales of the Colorado Group, except where these are obscured by soil, 

 debru, or scattered drift. The Yampa River passes through only the 

 northwestern corner of this part of Axial Basin, but, viewing the region 

 topographically, the most natural course for that river to run would 

 seem to be through the whole length of the basin, instead of cutting, as 

 it has done, through the elevated land that borders the basin on the 

 north, and which is composed of the comparatively hard sandstones of 

 the Fox Hills and Laramie groups. This eastern portion of the basin 

 is drained by the upper branches of Milk Creek, and a few other drain- 

 age-channels, which are mostly dry during a part of the year. 



The boundaries of the western portion of Axial Basin are much less 

 clearly definable than those of the eastern portion. In general terms it 

 may be said to be bounded as follows: On the east by Yampa Moun- 

 tain ; on the south by the water-shed ridge between the Yampa and 

 White Elvers ; on the west by Junction Mountain, in part, and in part 

 by Lily's Park. It is continuous with Snake Eiver Valley to the north- 

 westward, and on the north it blends, by a gradual rise, with the high 

 lands that lie between the valleys of the iSnake and Yampa Elvers. The 

 western portion of the basin is, therefore, much wider than the eastern 

 portion, and a very large part of it lies beyond the northern boundary 

 of this district. The portion that lies within the district has, like the 

 eastern portion, been primarily excavated out of the shales of the Col- 

 orado Group, but its surface is now occupied in very large part by the 

 friable strata of the Uinta Group, through which, here and there, the 

 underlying Colorado shales appear. Eesting upon the Uinta deposit 



