128 EEPOET UNITED STATES GEOLOGICAL SUEVEY. 



them, from their x)osition and cliaracter, as analogous to tlie Puerco 

 marls of New Mexico and Colorado. The series of upper sandstones and 

 shales reaches a thickness of about 600 feet. Within this region a num- 

 ber of volcanic eruptions have taken place. North and northeast of 

 Salt Wells several buttes occiu", forming prominent features in the 

 landscape. Essex Mountain is one of these. From its summit we can 

 trace, by the color, the extension of the Wasatch Grouj). At this lo- 

 cality the strata have assumed a horizontal position, farther north 

 a very gentle southerly dip. Toward the west the area of the group 

 is closed by the superposition of Green Eiver beds. East and north 

 the same strata spread widely. Following the trend of the outcrop- 

 ping volcanics we advance toward the railroad in a southeasterly line. 

 After crossing a creek, which on some maps is designated as Sulphur 

 Creek, we gradually rise to the highest elevations which the Wasatch 

 attains in his region. Descending from a north to south ridge we see 

 before us the wide expanse of Eed Desert. A perfectly level valley of 

 oval shape is surrounded on all sides by low blufis. Toward the north 

 the color of the soil is perfectly white, but farther south it tiu-ns to a 

 brilliant red. Not a drop of water is foimd in tha;t entire section of 

 country. The red color of the desert-like depression is derived from the 

 upper members of the Wasatch series. Northeast of Eed Desert we 

 find the extensive series of depressions which have been comprised 

 under the name of Shoshone Basin. This appellation is given as a i3urely 

 topographical one, without reference to the geognostic structm^e of 

 the region. We find northward of Trail Lake a number of others AYithui 

 the area of the same groui"). In this vicinity the strata are very reg- 

 ular in their arrangement. A very slight dip toward the basin, together 

 with a general inclination southward, may be observed, however. North- 

 west of Trail Lake, near the base of Station 21, the marls are again ex- 

 Pkosed. From a long distance, even, may they be recognized by their 

 characteristic coloring. Typical mauvaises terres are carved out of the 

 marls at this locality. 



Northeast of Trail Lake the stra,ta continue in regular succession, 

 showing a bright red color near the ujiper portions of the blufis. This 

 is due to the burning of coal beds. By this process the shales thus 

 changed have been rendered less liable to disintegration, so that the red 

 color is essentially confined to a narrow, almost horizontal band. A num- 

 ber of small lakes and several dry lake-beds were found here, still belong- 

 ing to the depression of the Shoshone Basin. Near one of these a large 

 number of mud springs were found, which shall be referred to again 

 below. So far as we could determine, the thickness of the u]iper portion 

 of the Wasatch diminishes considerably as we api^roach the Sweetwater. 

 Examining the most northerly outcrops of the group we find that it ends 

 in a succession of small bltifii"s as we reach the metamorphic and Prozoic 

 area. A little farther east, along the southern slope of the Sweetwater 

 Hills, the junction is obscured by drift and accumulations of santl. 



This latter feature is one which was very extensively noticed 

 throughout the Wasatch region. A broad belt of sand dunes stretches 

 diagonally across the southern portion of our district, ending at Sandy 

 Creek Pass. Traveling toward the eastern edge of the Wasatch expos- 

 ure, we find everything rendered indistinct by masses of loose drift scat- 

 tered over the valleys and blufis. West of Creston station we obtain a 

 comparatively good view of the lower portions of the group. Here the 

 sandstones are decidedly amplified as compared to those farther north, ■ 

 and the arenaceous shales and marls are well developed. Large masses 

 of crystallized selenite are scattered over the bluffs and hill-sides, com- 



