14 REPORT UNITED STATES GEOLOGICAL SURVEY. 



rises at the north side of Gray Hills and courses along the flank of the 

 hogbacks of Midland Flexure and thence parallel with the Grand Hog- 

 back to White River. This drainage carries a large amount of water in 

 the wet season, but it becomes entirely dry in summer. 



Below Powell's Park the blufis of the Green River Gronp come near 

 to White River almost all the way to its confluence with the Green, so 

 that between Powell's Park and the western side of Raven Park the 

 greater portion of the width of the valley is upon the northern side of 

 the river. Between Powell's Park and Coyote Basin the valley has con- 

 siderable width on the northern side, and at several places there are 

 considerable areas of irrigable land. 



Raven Park. — A comparatively small uplift, which is separate from, 

 but accessory to, the Uinta Uplifts, crosses the valley of White River 

 at a point southward from Midland Ridge, where it has brought up to the 

 surface the shales of the Colorado Group; and out of these shales 

 Raven Park has been excavated. The park lies mainly upon the north 

 side of the river; and since the Raven Park Uplift has a quaquaversal 

 dip, the park is wholly surrounded by an escarpment of Fox Hills 

 strata. The park is a small one; the river traversing its southern por- 

 tion, a comparatively large proportion of its surface may be reached by 

 water from irrigating-ditches leading from the river above its upper 

 limit. Raven Park, like the others before described, and like many 

 other portions of the valley, contains within its limits some of those 

 broad benches or table-lands that have been before mentioned. They 

 are above the reach of irrigating- waters and occupy a large portion of 

 the surface of this park. Aside from the action of White River, the 

 excavation of Raven Park has been mainly accomplished by an exten- 

 sive dry drainage-creek that has its rise many miles to the northward, 

 upon the slopes of Midland Ridge. For a distance of several miles 

 below Raven Park the river valley is moderately narrow, but still there 

 are some level bottom-lands on each side of the stream. Below this, 

 almost all the way to the western border of the district, the river runs 

 in an almost continuous, deep, narrow caiion, which it has excavated 

 out of the strata of the Green River Group. The walls of this canon 

 are always steep and often perpendicular. In some places they are 

 nearly a thousand feet in height above the river, and approach it so 

 closely that it is always difficult, and for many miles impracticable to 

 traverse it with a mule-train. 



Yampa River Valley. — The Yampa has its origin by numerous 

 mountain -brooks that rise among the granite gorges of the Park Range, 

 and also among the Cretaceous rocks that flank that range on the west. 

 Like White River, the Yampa is, in its upper portion, a clear, cold trout- 

 stream, its bed being paved nearly all the way from its source ^to its 

 mouth with smoothly-worn drift-pebbles. The Yampa has only two 

 tributaries in this district, worthy of note, that carry perennial water. 

 These are Williams Fork and Milk Creek, both of which will have fur- 

 ther mention on subsequent pages. 



Yampa Valley, like that of White River, has its parks and narrower 

 spaces of low lands, but it is most remarkable for its caiions; not so 

 much because it has caiions along its course as because that river 

 seems from a superficial or topographical view to run where nature had 

 placed especial obstacles in its way, apparently' giving no heed to the 

 favorable opportunities it seems to have had for pursuing a peaceful and 

 easy course. 



Between the eastern border of the district and the confluence of Wil- 

 liams Fork, the valley of the Yampa is a moderately broad one, the 



