GEOLOGICAL SURVEY OF THE TERRITORIES. 45 



Black's Fork for fourteen miles. This is a beautiful and fertile valley, 

 varying from three-fourths to a mile in width. Every foot of the 

 bottom land could be cultivated with ease, and Black's Fork would 

 supply, an abundance of water for irrigation. The soil, like that of all 

 the valleys of the Uinta range, is a rich black vegetable mold, which 

 always sustains a heavy growth of native vegetation. The creek itself 

 is fringed with a handsome border of cottonwoods and aspens ; spruce 

 and pine come in, which, mingled with the deciduous trees, give a pleas- 

 ant variety to the foliage. Each of the streams that flow down the 

 slopes of the Uintas separate into numerous branches, and between each 

 branch there is a dividing ridge which extends down from the moun- 

 tains and breaks off abruptly at the base. The Bridger group extends 

 up to the base of these ridges and juts up against the foot-hills. Then 

 come the grass-covered and woody ridges, which are composed of strata 

 .of yellow and green arenaceous clays, with thin layers of sandstone pro- 

 jecting from the sides. The grass and other vegetation covers the sur- 

 face so uniformly that it is difficult to find a connected section of the 

 strata, but it is probable that there are lower tertiary beds, which form 

 a portion of the coal series. 



Leaving Black's Fork we ascended the dividing ridge westward to 

 Muddy Creek, and followed an old trail just under the foot-hills of the 

 mountains. The elevation of the summit of the ridge is 7,857 feet. 

 This ridge is most beautifully diversified with groups of aspen trees. 

 The surface is covered with loose water- worn rocks, mostly the red 

 sandstones and quartzites that must have been drifted from the crest of 

 the mountains. On the west side of this ridge is a singular table-top 

 butte, with an elevation of 7,977 feet, and five hundred feet above the 

 waters of the Muddy, which flows along its western base. It is evidently 

 a fragment of an upheaved ridge of middle tertiary strata, inclining from 

 the mountains at a small angle. The southwest side is very abrupt, and 

 the strata are exposed so that a moderately good section can be studied. 

 The summit is covered thickly with water -worn boulders, which seem to 

 have lodged there on their way from the Uintas. The deposit of drift 

 is at least fifty feet thick, and the greatest accumulation of the boulders is 

 on the abrupt edge toward the ranges. Below the drift are alternate layers 

 of light-gray argillaceous limestone, sandstone, and laminated arenaceous 

 clays. In one of the upper beds of limestone is a thin seam of black 

 chert or flint, with fresh-water shells, and plants. A thickness of two 

 hundred feet of the base of the hill is composed of arenaceous clays 

 with a light pinkish tinge, which is peculiar to a vast series of beds 

 west of the rim of the basin. From the top of this butte the view is very 

 extended in every direction. To the south are the Uinta Mountains, 

 with the foot-hills or ridges gradually sloping down into the plains, 

 covered with aspen groves and pines, with here and there grassy, 

 meadow-like openings. To the west and north, as far as the eye can 

 reach, thirty to fifty miles, we see only the modern tertiary beds. These 

 all show a slight inclination from the range, with the southwest side of 

 the projecting ridges abrupt and denuded, and the northeast side 

 sloping gently down and covered thickly with grass. On one of the 

 little branches of the Muddy the carboniferous limestones crop out 

 somewhat obscurely, but sufficient to show that they exist underneath 

 this vast deposit of drift and tertiary strata. I have no doubt that the 

 entire series of unchanged beds known in this region, either do exist or 

 have existed on the flanks of the Uintas, although at this time they 

 may have been eroded away. We know that along the railroad, near 

 Aspen Station, the cretaceous rocks are brought to the surface, and in the 



