PEALE.] GEOLOGY GRAND RIVER. * 89 



lY. The valley of the Grand below the njonth of Roaring- Fork is only 

 about two miles long, the river again entering a cafion. At the head of 

 this eaiion the Eed Beds cross, aud are shown on both sides. The river 

 gradually bends and follows the strike, in a monoclinal, rift for six miles, 

 when it turns again aud cuts abruptly across almost at right angles to 

 the strike, flowing through a valley cut in the soft shaly beds that lie 

 just above the Dakota group. 



This valley is only a few miles in length, and in it the river is joined 

 by quite a large stream from the north, which flows along the eastern 

 base of the Cretaceous range, w^hich I have described as ending in the 

 plateau to the northwest. From this valley the river cuts through the 

 strata at right angles to the strike, and comes out into a broad valley, 

 • through which it flows for fifteen or twenty miles, and enters another 

 caiion, or rather caiion-like valley, cut in a plateau in which the beds 

 are almost, if not quite, horizontal. This canon is more or less persist- 

 ent until the river enters the valley in which it is joined by the Gun- 

 nison. The general course of the river lor about nineteen or twenty 

 miles is south 70O-75° west. At the head of the valley the blufl's are 

 almost vertical, and, indeed, in some places, the cliffs, as seen in certain 

 lights, appear to overhang. At the point where the course changes 

 to the southward, the valley is wider, and the Grand splits, forming 

 islands in the midst of the river. This is northwest of station 50. 

 The plateau here, between the Grand and Plateau Creeks, is narrow, and 

 has in reality degenerated into a ridge from which the basaltic capping 

 has been removed. 



Eeturning to the valley above the canon, we see that it is from fifteen 

 to twenty miles in length, and that the drainage on the south is princi- 

 pally through two streams, one in the eastern portion and the other 

 (Xorth Mam Creek, see map E) on the western side. They rise in the 

 plateau forming the divide between them and the head of the North Fork 

 of the Gunnison. The eastern branch is formed by two streams, whose 

 courses are almost parallel. Between the East Fork and Eoaring Fork 

 there is a smaller creek (c creek. Grand Eiver), which rises in a 

 mass of rounded hills, which I referred to when speaking of the hog- 

 backs on the west side of Roaring Fork. Between this creek and the 

 plateau south of the caiion theie are several folds, the axes of which 

 are parallel, each being northwest and southeast. 



The rocks underlying the valley are all of Cretaceous age, capped 

 irregularly in places with basalt, especially on the divide. Here the 

 strata are almost horizontal, inclining, if at all, only a few degrees 

 toward the west in the eastern portion. 



The line of hog-backs before referred to, extending along the lower 

 side of the Grand from station No. 16, tlirough station 18, and cross- 

 ing the river, forms the side of a synclinal fold, the axis of which is, 

 partially at least, occupied by a creek (c. Grand River). The dip of 

 the strata is southwest, inclining at an angle of about 15° ; this increases 

 as we go toward the Grand, being about 60° there. 



Station 20 is on the opposite side of the fold, the dip of the sandstones 

 there being northeast at an angle of 15° to 20°. From station No. 19 

 to 22 there is a mesa covered with basaltic bowlders. I am inclined to 

 think also that there is a capping of the same material. The bowlders 

 are derived from the hills near the divide. The mesa is about a mile 

 wide and slopes gently toward the Grand. It is about 400 feet above 

 the valley of the creek at the forks below station No. 19. At station 

 tion No. 22 it is 800 feet high. 



Between the forks of the large creek east of North Mam Creek, the 



