kkduch.] EAST OF WIND EIVER EANGE TEIAS. 81 



Within oiir district tlie Triassic beds have reached a good development 

 and are exposed very frequently. One of the best known occurrences 

 east of the Wind Eiver Eange is that of Eed Canon. If we stand on 

 Twin Peak and look towards the northeast, we will have before us a 

 gradual slope down to the narrow valley of Deep Creek. Bising imme- 

 diately upon the eastern bank of this small stream we see a steep red 

 wall, continuing for the distance of several miles. The remarkable bril- 

 liancy of color renders it a very striking feature of the landscape. An 

 examination of this wall will reveal the fact that it is composed almost 

 entirely of bright red shales and sandstones. Near the base of the series 

 we rind red sandstones, highly argillaceous and rather thinly bedded. 

 A little higher up the strata grow thicker and somewhat coarser. They 

 are separated from each other by thin layers of very fine-grained shale. 

 Thus far we have seen about the lower third of the group. Above that 

 thick beds of red shale set in, weathering in characteristic forms. Numer- 

 ous vertical seams aid the progress of erosion. Near the top of these 

 shales we find thin beds of sandstone, more or less coarse grained, usu- 

 ally red, but sometimes pink and white. Throughout the shales we meet 

 with narrow "ledges" composed of very compact gray and yellow dolo- 

 mite. Small cavities and seams in them are lined by crystals of the 

 same mineral. Above the shales and thinly bedded sandstones, we 

 again observe massive strata of the latter. Shales close the group. 

 Both near the base and the top, isolated layers of pink and white sand- 

 stones may be noticed. As a rule, we may accept two horizons for 

 coarse-grained sandstones, although they are essentially a local product. 

 Near the base, and again in the upper third of the series, they are found. 

 The thickness of the Triassic beds at this locality may be regarded as 

 about 800 feet. 



In this region, as well as elsewhere within our district, we find the 

 Eed Beds directly overlying the Permian strata, and covered by Jurassic 

 limestones. From the section previously given, it will be seen that the 

 Triassic beds (1c) are perfectly conformable with both under and overly- 

 ing groups. Following the outcrop southward from Eed Canon, we 

 find that the red sandstones and shales retain a prominent position until 

 closely approaching the Sweetwater group. There the southwesterly 

 direction of the anticlinal axis causes a preponderance of palaeozoic 

 rocks, the greater portion of the younger groups disappears, and the Eed 

 Beds are crowded into a narrow space. Finally they disappear under 

 the Tertiary strata, not again to be exposed until many miles farther to 

 the eastward. North of Eed Canon the Triassic strata first make a turn 

 which brings them high up on the eastern slope of the third chain. 

 Eeceding again they form a series of bluffs along the base of this chain 

 until they pass beyond the limits of our district. So far as the out-crops 

 have been described the strata have a general dip east and northeast, 

 amounting to 32° to 36°. At the highest point reached by them this 

 angle is somewhat increased. 



We find that along this line of exposure the Triassic strata presents 

 but a small area. Eapidly removed by erosion on the west side, they are 

 covered by younger formations a short distance eastward. Eeverting 

 again to Section I, it will be seen that the Eed Beds form prominent bluffs 

 on either side of Sheep Mountain. On the east side they present a 

 steep, quadricircular wall similar to that on Deep Creek. From there 

 southward the bluff-line follows the strike of the Carboniferous lime- 

 stones, until finally both are lost under the beds of the Sweetwater 

 Group. North of Sheep Mountain we find different conditions, however. 

 A thickening of the entire series is noticeable, which reaches over 1,000 

 feet. Following down Twin Creektoits junction with the Little Popo-Agie, 

 6 G S 



