270 Tertiary. 



The Pliocene or Salt Lake Group in Bear river valley consists of 

 3^elIow sands and marls, white limestones and shales, and pea green 

 shales and sands. The thickness is estimated at from 600 to 700 feet. 



The Salt Lake Group or Pliocene of Cache valley is succeeded by a 

 later Pliocene deposit, for which Dr. Peale proposed the name Cache 

 Valley Group. The beds near the center of the valley deposited 

 by the lakes, and still remaining in horizontal position, are those to 

 which he applied this new name, but without more reasons than he 

 adduces it would have been just as well not to have proposed it. 



F. M. Endlich found east of the Wind River Range a series of varie- 

 gated, arenaceous marls, resting upon the yellow sandstones of the 

 Laramie Group. These are of the age of the Lower Wasatch or Lower 

 Eocene. They are nearly horizontally stratified, and are carved into 

 typical "Bad Lands" by fluviatile erosion. A variety of colors 

 presents itself in these marls. Gray and reddish-bi'own predominate, 

 interchanging, however, with yellow, white, greenish, and maroon. 

 Without any apparent separation of strata, these colors and shades 

 form bands resembling well-defined bedding. Rapidly denuded by 

 erosion, the slopes presented b}' these marls are generally entirely bare 

 of vegetation. Thin bands of highly argillaceous sandstones, occurr- 

 ing sporadically within the series, sometimes give rise to the forma- 

 tion of low regular bluffs. These marls southeast of Beaver creek, 

 have a thickness of 450 to 500 feet. They are supposed to be parallel 

 with the Puerco marls of New Mexico and Colorado. The}^ are suc- 

 ceeded by the yellow sandstones and shales of the Upper Wasatch 

 Group. 



An extensive section of the Wasatch Group may be oiitained north of 

 Salt Wells. The lower marls reach a thickness of 600 to 700 feet, and 

 the upper sandstones and shales attain a thickness of about 600 feet. 

 A number of volcanic eruptions have taken place in this region. 

 Several buttes occur, from one of which called Essex mountain, the ex- 

 tension of the Wasatch Group may be traced by its color. The Red 

 Desert of this region is derived from the upper members of the 

 Wasatch Group. Not a drop of water is to be found in this desert. 

 The thickness of the Upper Wasatch diminishes in the direction of the 

 Sweetwater. 



The Wasatch Group is succeeded by the Green River Group. 

 Packer's creek flows in a southerly direction into Bitter creek, a short 

 distance east of Rock springs. West of it there is a high ridge com- 

 posed of the light Green river shales. The strata have a gentle dip to 



