PEALE.j GEOLOGY NORTH FORK OF THE GUNNISON. 101 



streams heading in the plateau, flows for a short distance through a 

 beautiful grassy valley, from which the country on the west rises in a 

 plateau which is timbered on the slopes. 



At the lower end of the valley the stream gradually cuts deeper and 

 deeper into the sandstones, until, at the point where it meets Anthracite 

 Creek, it is about a thousand feet below the general level. All the 

 branches here, even the smallest, cut these canons, leaving mesas or tables 

 between, in which the strata are nearly horizontal, thus giving them 

 about the same general level. 



After the union of the two main creeks, the North Fork flows a little 

 south of west, almost at right angles, to the former courses, in a canon 

 which is from 1,500 to 2,000 feet deep. This canon is about fifteen miles 

 long. In the lower part the river gradually turns to the southward, 

 finally emerging into a rather broad, open valley extending on the lower 

 side to the foot of the hills on which stations 38 and 39 are located. 

 The vallej 7 becomes wider as we go toward Smith's Fork. It is compara- 

 tively open, being broken only by low hills or buttes of yellowish and 

 gray shales, all belonging to the Cretaceous formation. These buttes 

 have a scattered growth of stunted cedars and sage-brush. The soil is 

 impregnated with alkali, and generally sterile. The small streams cut 

 deep gulleys in the soft beds. As the river emerges from the canon the 

 mesas on the south side end abruptly in steep bluffs, just north of 

 station 39. Stations 38 and 39 belong to the tracbytic group, to which 

 I have already so often referred. They are beautiful examples of moun- 

 tain forms, rising in sharp conical points. Station 38 rises 4,000 feet 

 above the general level of the valley which it overlooks. As already 

 described, there is a gradual slope from the Gunnison to Smith's Fork, the 

 sandstone of the Dakota group forming the floor. Crossing Smith's Fork, 

 the softer beds, which we have already described, form lines of buttes. 

 Along the North Fork there are outcrops of black shales, in which the 

 general dip is to the northeast. On the north side of the river is a series 

 of terraces sloping from the basaltic- capped mesa which here forms the 

 divide between the Grand and Gunnison Rivers. 



Leaving the mesa caiion the North Fork turns still more toward the 

 south, and flows southwest to within about four miles of its mouth, when 

 its course becomes due west. In this valley the river winds in graceful 

 curves, outlined in the most distinct manner, as seen from the moun- 

 tains and plateau, by the fringes of cottonwoods on its banks. Just 

 before it turns to the westward it enters a caiion. The walls, at 

 first, are mere bluffs, cut in the black shales that lie immediately above 

 the Dakota sandstone. By the time it joins the Gunnison it has cut 

 pretty deeply into the Dakota group. The river in this part of its 

 course is parallel with Smith's Fork, and joins the Gunnison in the caiion 

 at right angles to the former course of that stream. The Gunnison, 

 however, turns and flows to the westward in the direct line of the North 

 Fork. 



This part of the caiion of the Gunnison is ten miles in length and with 

 walls from 400 to 500 feet high. Although in many places the bluffs rise 

 in sheer precipices from the river's edge, in others there are alluvial 

 bottoms, sometimes on one side and sometimes on the other. The general 

 course is about due west. 



Fig. 3, Plate VIII, represents a section across the Gunnison through 

 the line E F, on map B. At a it cuts the river just above the mouth of 

 Smith's Fork, before it leaves the granitic caiion, and at d it cuts the 

 river below the mouth of the North Fork. It will be seen that there is 



