86 GEOLOGICAL SURVEY OF THE TERRITOKIES. 



The area drained by tliese branches includes about 1,300 square 

 miles. 



The country included is generally plateau-like in character. This is 

 more apparent to the westward, and in the divide between the Grand 

 Eiver and the North Fork of the Gunnison. The general elevation of 

 the plateau is from 9,000 feet to 11,000 feet. 



In the eastern portion, from the Eagle Eiver to a short distance west 

 of Roaring Fork, are rolling hills covered with scrub-oak {Quercus alba), 

 cotton-woods {Populus tremuloides), and stunted cedars {Juniperus occi- 

 dentalis). The latter was most abundant on the lower slopes, and 

 seemed to thrive best on soil derived from the breaking down of the 

 shales in the upper part of the Cretaceous and Tertiary formations. The 

 rocks throughout this region were mostly of Tertiary age, capped in 

 places by basalt. The general geology, however, will be dwelt on as 

 we proceed. 



The course of the Grand, from the mouth of the Eagle to the mouth 

 of Eoaring Fork, is south 60° west. Most of this distance, sixteen miles 

 in an air-line, the river is in caiion, the head of which is a little over three 

 miles below the Eagle. It is probably impassable to travel, the sides 

 being very steep. There is no Indian trail following the course of the 

 river. Mr. Marvine's party kept on the hills some distance back from 

 the edge on the northern side, and we followed an Indian trail across 

 the hills to a stream which joins the Grand at the head of the caiion. 

 This trail seemed to be much used and leads across to Eoaring Fork, 

 which it strikes above the mouth of Eock Creek, a branch rising in the 

 Elk Mountains. 



The valley above the caiion is about three and a half miles in length, 

 and although wider than the valley of the Eagle just above its mouth, 

 is still comparatively narrow. On the north side are limestone slopes, 

 and on the south low, rounded hills of the gypsiferous beds. At the 

 head of the canon and forming the gateway, as it were, are beds of mas- 

 sive limestone, probably of Carboniferous age. They dip to the north- 

 east, inclining about 20°. Farther along in the caiion there may be out- 

 crops of older beds, which can be determined only by following the 

 bluifs close to the river. The hills on the south side of the caiion are 

 capped with a black vesicular basalt, which rests immediately on the 

 Triassic red sandstones. The dip of these beds I was unable to deter- 

 mine, but they are probably conformable to the layers beneath. 



The creek up which the trail led, after leaving the Grand, joins the 

 river by cutting a small canon through limestones similar to*those at 

 the head of the canon of the Grand. These beds are somewhat mas- 

 sive, and above them are blue limestones with interlaminated sand- 

 stones passing into gray and white sandstones, with yellow and black 

 shaly beds above. These are beneath tlie pink gypsiferous beds'out- 

 cropping farther up and corresponding with those on Eagle Eiver. 

 Still farther up stream the Eed Beds appear, the line of outcrop crossing 

 the creek near its head. 



Leaving this creek, we crossed to the waters of Eoaring Fork, the first 

 stream reached being a branch joining it about two miles below the 

 mouth of Rock Creek. The country between the Grand and Eoaring 

 Fork here is a rolling plateau covered mostly with a growth of scrub- 

 oak. The plateau is capped with a black vesicular basalt, which in 

 places is worn away, exposing the red sandstone beneath. The 

 head of the creek is in canon in which the Cretaceous beds are shown, 

 dipping to the southwest. Station No. 11 was almost on the line be- 

 tween the top of the Eed Beds and the overlying stata. Farther down 



