92 GEOLOGICAL SURVEY OF THE TERRITORIES. 



the G-rand and its branches cut fearful-looking chasms in the soft rocks. 

 Looking down upon them it is hard to trace the courses of the streams, 

 as it appears to be an inextricable maze of gorges. 



There is great variety in the colors ; reds, greens, grays, yellows, 

 mingle with chocolate-browns, and white, in parallel lines, which repeat 

 themselves in the different layers. 



At the head of the canon of Plateau Creek the Indian trail we had 

 been following leaves the creek, goes up Mesa Creek, and skirting the 

 edge of the mesa, leads down into the valley of the Gunnison. • 



The course of Grand Eiver below the mouth of Plateau Creek is gen- 

 erally southwest, and sometimes due south. • 



It flows in this direction until it comes out into. the broad valley, in 

 which it is joined by the Gunnison. It emerges from the canon by cut- 

 ting its way across a line of hog-backs, almost at right angles to the 

 strike of the strata, the beds dipping about northeast at an angle of lOo 

 to 15°. 



Plate VI represents the blnff on the north side of the river, as it comes 

 from the canon into the broad valley. 



The numbers in the following section correspond with those in the 

 illustration. 



BASE. 



1. Black and yellow shaly beds. 



2. Yellow sandstone. 



3. Yellow shaly beds. 



4. Sandstones. ^^ 



5. Shales. 



6. Sandstone with pinkish hue. 



This section was made from the opposite side of the Grand, and could 

 not, therefore, be made in greater detail. The beds were measured by 

 angles taken with the gradienter. The height of the bluff as thus deter- 

 mined is 1,890 feet. On the south side of the river the inclination of 

 the beds causes them to disappear, while higher ones show beneath the 

 basalt of the mesa. The slopes, reaching from the edge of the mesa in 

 terraces, are covered with basaltic bowlders, among which we found 

 numbers of moss-agates (none of good quality, however) and pieces of 

 chalcedony. 



West of the line of hog-backs, which extend toward the northwest 

 from the Grand, the valley is about eighteen miles in width, reaching to 

 the northwest as far as could be seen. Near the Grand, before the 

 Gunnison comes in, it is very flat and covered with spots of alkali. On 

 the sonth side of the Grand, in the angle between it and the Gunnison, 

 are terraces, the first of which is one hundred feet high, and the second 

 nearly two hundred feet. The contrast between the two rivers is quite 

 marked. The Grand has nearly twice the volume of the Gunnison, and 

 and carries a vast quantity of mud with it. Wherever we reached the 

 Grand throughout the entire season it was muddy. The reason is, that 

 along the river there are many exposures of soft shales and clays. 

 The Gunnison, on the other hand, is a clear stream, and remains so except 

 when there are heavy rains, when it becomes very turbid in the lower 

 portion of its course. 



The divide between the Grand and Gunnison Elvers has been so often 

 referred to in this chapter that only a few more words are necessary to 

 complete its description. In the Elk Mountains the line of the water- 

 shed is very irregular, the mountains rising in sharp peaks, at the bases 

 of which the streams head in auij)hitheaters, sharp ridges connecting 



