peale.] GEOLOGY TRIASSIC STRATA — GRAND RIVER, &C. 123 



anticlinal, which is shown at a a in Fig. 1, Plate III, the RedBedsforining 

 the top of the bluffs on either side of the river, as shown in the figure. 



Grand River. — From the mouth of Eagle River the Red Beds cap the 

 bluff for some distance, when the line of outcrop crosses to the south- 

 ward and afterward to the east, joining the line continuing westward 

 from h creek (map A), thus forming an isolated area of red sandstones. 

 Between the Grand and Roaring Fork, there is another patch of Red 

 Beds, which is partially concealed by an overflow of lava. On the west 

 side of Roaring Fork we have the Red Beds showing in the hog backs. 

 Their thickness here is about 1,500 feet. They dip south 75° west, at 

 an angle of 30°, below station 14. The upper part of the series here has 

 layers of pink conglomerate sandstone. 



As we go down Roaring Fork the strike curves to the westward, and 

 the Red Beds disappear beneath a layer of volcanic rock which covers 

 the hills here. They re-appear on Grand River on the south side, a short 

 distance below the mouth of Roaring Fork, forming high bluffs, that rise 

 500 or 000 feet above the level of the river. The Grand then gradually 

 cuts into thered sandstones, following the strike, which is about north 60° 

 west for nearly four miles in an air-line, forming the base of the hog- 

 backs that here exteud along the southern side of the Grand. The 

 river then cuts across the strata, flowing out into higher and softer beds, 

 while the Red Beds cross iuto Mr. Marvine's district. From this point 

 to the mouth of the Gunnison there are no exposures of the Triassic 

 sandstones. 



Gunnison River.— The Triassic sandstones do not appear on the Gun- 

 nison River until the lower half of the Grand Caiion is reached. They 

 seem to increase gradually in thickness, although the total thickness 

 attained in the canon is not very great. They rest immediately on the 

 granite shelf forming the edge of the canon below station No. 80. The 

 art- a occupied by them along this canon is indicated on map B. At 

 station 80, the anticlinal axis occupied by the river is very evident. 

 It is shown in Fig. 1, Plate VII, at a. Leaving the canon the river cuts 

 across the northern end of the anticlinal, and, turning to west, flows 

 out into the soft shales of Cretaceous age. In the second or lower caiion 

 the river cuts down through the Dakota group and the Jurassic layers, 

 and partially into the Red Beds. 



The top of the series here is a pink sandstone, from 30 to 40 feet in 

 thickness. The thickness of the red sandstones varies. Below station 

 60, where the pink sandstones were measured, the thickness exposed is 

 about 150 feet. They are massive and present all the characteristics 

 that the Red Beds east of the mountains do. They dip approximately to 

 the eastward, the angle decreasing as we leave the river and increasing 

 to the west. The river winds through the caiion in large curves that 

 almost meet each other. Whenever the curve is to the westward the 

 led sandstones are cut into most deeply, and when the curve is in the 

 opposite' direction the Red Beds, if exposed at all, are only cut into 

 slightly. This causes the areas of Triassic age to appear in patches 

 along the course of the river. All the streams joining the Gunnison 

 from the west cut profoundly into the strata, and near their sources, 

 may have outcrops of Pre-Triassic layers along their courses. I have 

 already referred to the fact that the Gunnison River at this point fol- 

 lows a rift or break, which was probably caused by a monoclinal fold. 

 Two sections across this are shown in Figs. 1 and 2, in Plate IX. At 

 first the fold as shown in Fig. 1 is not very marked. It gradually 

 increases, however, and below the mouth of the Gunnison is as repre- 



