370 REPORT UNITED STATES GEOLOGICAL SURVEY. 



and the stream is freed from its rocky inclosure. The distant view ob- 

 tained from liere is magnificent. ^Ve are not only interested, in the great 

 gorge from which the Green River emerges into the broad expanse of a 

 valley, but we can also trace the stream in its winding course far to the 

 south, and have a fine view in the northwest, the Uintah Mountains, 

 ■with their lofty snow covered peaks, presenting a spectacle rarely 

 equalled. 



In describing the features of an almost totally unknown country, it is 

 necessary to give greater detail than the country would sometimes seem 

 to deserve, inasmuch as its value, practical or otherwise, must l)e deter- 

 mined. We would, therefore, be in error were we to omit allusion to a 

 peculiar and interesting feature connected with the great Yampa Pla- 

 teau. This feature is a well-defined, regular line of hogback hills which, 

 about three miles north of the northern plateau rim, stretch like a wall 

 around the great plateau (see Plate XXIII,) cut only here and there 

 by the drainage which has its source between the hogback hills and 

 the plateau itself. 



From the connection that can be traced between the highest portion 

 of Midland ridge and the hogback hills, it seems evident that from the 

 hogbacks which present now steep faces towards the equally eroded 

 faces of the great plateau there once existed between them a continuous 

 surface which has been eaten away by erosion, leaving it with its present 

 shape. Submitting all theories on the subject to the geologist for dis- 

 cussion, I will simply mention its present topographical appearance. 



The wall-like barrier with which the hogback hills, in a curved line, 

 circumscribe the plateau from Weary-mules-wash to within a few miles 

 of the western end of the plateau is singularly striking in appearance. 

 The hogbacks are really inclosures of a series of more or less well-ex- 

 pressed mountain basins, which lie along the debris slopes and spurs of 

 the great Yampa Plateau. The hogbacks are also frequently broken by 

 washes through which the drainage during winter and spring time finds 

 its way out of the basins. 



The" largest of the amphitheatres produced by the eccentricities of 

 erosion lies directly north of Midland ridge (see Plate XXIII,) which 

 is only the eastern although somewhat lower portion of the Yampa 

 Plateau itself. This basin is thoroughly amphitheatrical in shape and 

 is perhaps 10 miles long, from east to west, and 3 miles in width. A 

 gentle but very even rocky slope, with deeply cut drainage fissures in 

 it, descends from the debris of the plateau walls to the foot of the hog- 

 back hills. The exposed faces of the plateau as well as those of the 

 hogbacks consist of red sandstone, and in consequence of this the brick- 

 colored faces of these exposures contrast strangely with the gray and 

 dull color of the surrounding scenery. 



YAMPA RIVER. 



This stream excels its sister stream the White Eiver, not only in its 

 scenery, but also as to its pasturage and quality of such agricultural 

 area as under the most favorable circumstances this sterile plateau 

 country affords. Latitude 40° 30' forma the line along which, with re- 

 peated crossing and recrossing, the Yampa Eiver flows for 80 miles 

 to the westward. The stream indeed shows a direct westward ten- 

 dency from the very point where it first assumes the importance of a 

 river, which is in longitude 107"^; thence flowing westward to its junc- 

 tion with, the Green River, which is IJ miles west of meridian 109o. Its 

 total length from latitude 107"^ to the Green River, is about 100 miles in 



