426 GEOLOGICAL SURVEY OF THE TERRITORIES. 



the north side of the river is concerned. The flat plateau ends in a very 

 well-defined terrace, on an enormous scale, ten miles long and 1,800 to 

 2,000 feet high. In its place there is a lower sloping plateau, or long 

 hog-back, with its edge at the Gunnison Eiver, and line of greatest de- 

 pression in the valley of the North Fork of the Gunnison. This is a 

 true sloping plateau, its surface being perfectly flat and unbroken, with 

 the exception of the caiions of Smith's Fork and Dry Canon, which have 

 a course nearly parallel to that of the Gunnison above station 80. These 

 streams have many small gullies coming into them from the south, but 

 none at all from the north. The line of greatest slope of this plateau has 

 a direction slightly west of north. This plateau contains no water, and 

 the vegetation consists of the pihon pine, cactus, sage, and scrub-oak, a 

 marked difference in character from the plateau just east. This differ- 

 ence is owing in part to the greater slope of this plateau, thus carrying 

 the water off more rapidly, and in part to the less elevation. The 

 highest part, the edge, at the caiion of the Gunnison, is 8,600 to 9,000 

 feet, while the valley of the North Fork, the lowest part, is o,400 feet. 

 The character of the canon on the north side, as far down as station 

 80, is similar to that above, both geologically and topographically. 

 The stratified beds occupy 1,000 to 1,200 feet, with the same marked 

 bench, and the precipitous caiion in gneiss below. On the south side, 

 however, the top of the canon is lower than it is above station 77, 

 and the caiion is cut entirely in gneiss. The plateau on the south side 

 is nearly horizontal, with a slight slope to the west. 



At station 80 the river turns abruptly toward the north, and flows 

 in 'the direction of the greatest slope. Between station SO and the 

 mouth of the North Fork it has most of its fall. On the east side of the 

 river the character of the caiion is not materially changed until the 

 mouth of Smith's Fork is reached. On the west side, however, the 

 plateau ends abruptly opposite station 80, and a hog-back ridge of 

 stratified rocks, clipping steeply to the west, forms the upper part of 

 the west wall. This wall is much lower than that on the east, and is no- 

 where more than three miles thick. Beyond it is the broad, flat valley 

 of the Uncompahgre, at as low or lower elevation than the Gunnison. 



Between stations 80 and 81, the two parts of the caiion are very 

 strongly marked, showing a canon within a caiion. The caiion in 

 gneiss is merely a narrow cleft in the rocks, with smooth, vertical sides, 

 between which the river rushes down, its surface white with foam. At 

 the mouth of Smith's Fork, the caiion in gneiss is but 300 feet deep, 

 while the stratified rocks rise up to nearly a thousand feet. Just below 

 this point it runs out of the gneiss, and the rest of its course is in strati- 

 fied rocks, in which its 6haracter is entirely different. It no longer 

 rushes madly along, but meanders about in the broad bottom from one 

 wall to the other, leaving, now on this side, now on that, broad patches 

 of beautiful bottom-land. This character of caiion, similar to the lower 

 or Unaweep Canon, continues as far as station 83, where it terminates 

 abruptly. 



The appended list of elevations in different parts of this caiion give 

 an idea of its dimensions : 



HeigM of the icalls of the Grand Caiion of the Gunnison, at different points. 



At the head, near the mouth of Mountain Creek: 



Feet. 



At level of the river a 7, 200 



Top of plateau on north side of the river t 8, 800 



Height of canon wall 1, 600 



