feale.1 GEOLOGY GUNNISON CANON SMITH'S FORK. 97 



The country between Lake Fork and the Uncompahgre River is rough 

 and rugged. The streams cut deep canons to join the Gunnison. 

 Mountain Creek, Blue Creek, and Cebolia Creek are the principal streams 

 draining this region. Blue Creek, to which 1 have just referred, is placed 

 on Gunnison's map, as a branch of Cebolia, whereas it is a tributary 

 of the Gunnison. 



The mesas are found on Mountain Creek, and until we reach Cebolia 

 creek. Here we meet with cretaceous shales, seeming to be horizontal, 

 and resting on granite. The granite in places has trachyte resting on 

 it. I noticed it on the hills east of Cebolia Creek. 



The great caiion of the Gunnison is about fifty miles long. In it the 

 course of the river at first is west; it gradually changes toward the 

 north, and at station 80 flows northwest, gradually becoming due north, 

 which course it keeps rather uniformly to the month of the North Fork. 



From the head of the canon to the mouth of Smith's Fork the 

 main |)ortion is cut in dark micaceous schists. It has its great- 

 est depth, perhaps, opposite station 77 ; th.e height from the water to 

 the top of the mesa on which the station was located being about 

 3,000 feet. The granitic portion is about 2,000 feet deep. It was, 

 of course, impossible to reach the edge of the river while in the canon, 

 so that these figures are not perfectly accurate. They are obtained 

 by comparing the heights of stations 77 and 78 with that of camp 

 No. 53, on Cebolia Creek, about one mile above its mouth, and allow- 

 ing for the fall of the river between the two points. The error, if any, 

 would, therefore, be very small and in favor of greater depth. 



The section across the river, through stations 77 and 78, is shown in 

 Figure 2, Plate VIE. On the west, side of the river is a plateau about 

 four miles in width and thirteen miles long. Its elevation above 

 the river is 2,500 to 3,000 feet. It is composed of schists, and the top 

 seems to have a gentle slope to the eastward. It seems to have had in 

 places a capping of trachyte. 



East of Cebolia Creek, on the granite hills, a portion of this trachyte 

 still remains. To the northward the plateau runs to apoiut, thetermina- 

 tion being marked by ahigh conical point of granite. Beyond this, are red 

 sandstones (Triassic), with superimposed Jurassic and Cretaceous strata, 

 as seen from station No. 80, on the opposite side of the river. Fig. 1, Plate 

 VII, shows a section through station 80. It will be seen that the granite 

 forms a sort of shelf along the river, on which the sedimentary forma- 

 tions rest, having bluff-like edges a short distance farther back. These 

 beds incline at a small angle (about 5°), causing the country to slope 

 gently toward Smith's Fork, which here flows almost parallel to the 

 Gunnison. The illustration, Fig. 1, carries the section across Smith's 

 Fork. Beneath station 80 is an outcrop of the Red Beds. Where the 

 section crosses Smith's Fork, the latter stream does not cut below the 

 Dakota group (No. 1). Near the mouth, however, it cuts through the 

 Red Beds reaching the granite. 



Smith's Fork joins the Gunnison as the latter emerges from the gran- 

 itic portion of its canon, and cuts across the strata into the Cretaceous 

 sandstones. It rises in the group of trachytic peaks that 1 have already 

 referred to as terminating the Elk Mountains to the westward. Before 

 it leaves these peaks there are outcrops of Cretaceous shales seen near 

 the water's edge, on the main creek at first, but afterward spreading out 

 and covering wider areas. After it is fairly out of the mountains it flows 

 across the Upper Cretaceous formation, and gradually cuts through the 

 sandstone of No. 1, which forms bluffs extending along its course from 

 the mouth of the Southern Fork to the mouth. (See inaj) B). 

 7 H 



