98 GEOLOGICAL SURVEY OF THE TERRITORIES. 



The Southern branch of Smith's Fork rises in a comparatively open 

 country, opposite the creek which forms the boundary of the last mesa 

 on the upper side of the Gunuison. It lies almost entirely in the Upper 

 Cretaceous formations, which are exposed in low hills covered with 

 cedars and sage-brush. At one place it cuts a caiion through No. 1, from 

 which it comes into the upper beds, not touching the Dakota group 

 again until it joins the North Fork. This canon is only two miles long, 

 and must have been determined by a fracture caused by folding. On 

 the west side the inclination of the sandstone is only 5°, while on the 

 east it is 15° to 20°, In the latter there is only a small triangular area 

 of No. 1 exposed, the base of the triangle resting on the stream. 



Opposite the mouth of this fork is a hill of trachyte, which may have 

 had something to do with the fold we have noticed. About three miles 

 above this hill, on the north side of the North Fork, there is a finger-like 

 rock (trachyte) projecting from the Cretaceous shales. From the junc- 

 tion of the forks to the mouth is a distance of thirteen miles, in which the 

 river is in caiion or a canon like valley, the height of the cliii'son either side 

 ranging from about two or three hundred feet at the head to nearly fifteen 

 hundred near the mouth. The walls are very nearly vertical, but they 

 do not rise immediately from the edge of the river, there being a valley 

 between the bluffs, about a quarter of a mile wide, which continues al- 

 most to the mouth of the river as a fertile bottom, groves of cottonwoods 

 fringing the banks of the stream. 



Near its mouth the river cuts a narrow gorge in the granitic rocks, 

 the level of the river being some distance below the general level of the 

 bottom of the caiion. Map B shows the geology of the region about the 

 mouth of Smith's Fork, and the lines of the sections H, C-, K, L, and I. 



The North Fork joins the Gunnison three and a half miles below the 

 month of Smith's Fork. ^ The course of the Gunnison between the two 

 streams is nearly due north. On station 81 the strata have a dip 

 east of north, while on the opposite side of the Gunuison the inclina- 

 tion is west of north, showing, what is plainly seen from the station, that 

 there is a curving of the strata. Smith's Fork flows almost in the direc- 

 tion of the strike of the beds on its aight side, while the Gunnison, jafter 

 the union of the two, cuts across the strata almost at right angles to 

 the strike. 



Where the North Fork comes in the course is again changed, the river 

 then taking the course of North Fork, which is nearly due west. 



The North Fork is the principal tributary of the Gunnison, its general 

 course, as I have already indicated, being about west. It drains a 

 large area, and is formed by two branches, one heading opposite Rock 

 Creek and other tributaries of the Grand, and the other having its 

 sources opposite Ohio Creek and Slate Eiver, in the group of trachytic 

 peaks to which I have already alluded several times. 



The latter branch, on the map accompanying a report of Lieutenant 

 Euffner,* at its head is called Anthracite Creek, and a short distance 

 below Bah River. The name " Anthracite " was given from the discovery 

 here by prospectors of a bed of coal, of excellent quality. I will refer 

 to this coal again in another part of the report. We have retained the 

 name, but instead of applying the name to only a portion of the creek, 

 have given it to its entire length. In regard to the Bah, Mr. H. G. 

 Proutt says, "The Bah is said to empty into Grand (Gunnison) River 

 below the Lake Fork." He therefore evidently refers to the North Fork, 



* Report of a Reconnaissance in the IJte Country, in 1873, by Lieut, E. H. Ruffner, Corps 

 of Engineers, 

 t Ibid, page 40. 



