302 DESCRIPTIVE GEOLOGY. 



The upper valley of the eastern branch of Lake Fork has the usual 

 gateway at its mouth, formed by the closing together of the outcrops of 

 Triassic sandstone ; the valley above for a few miles is, however, wide and 

 comparatively open, and the gateway less pronounced than that of Antero 

 Canon, so that the outcrops are more concealed by surface accumulations 

 and afford a less continuous section. Through this valley runs the Indian 

 trail from the Uinta Reservation to Fort Bridger, already mentioned as cross- 

 ing the summit at Jones's Pass. From its mouth out upon the Tertiary 

 plain, to the east of the stream, extends a long narrow ridge, formed by a 

 lateral moraine, several hundred feet in height near the mountains, and 

 apparently extending 5 to 10 miles away from them. The first outcrop 

 found under the Tertiary beds in ascending the caiion was that of a bed of 

 white sandstone of about 500 feet thickness, standing at an angle of 25° 

 south, with a strike nearly due east and west. Below this, with the excep- 

 tion of a 40-foot bed of harder, more compact sandstone, no outcrops were 

 found till beds of 100 feet of blue limestone were found in the open valley 

 above, while at the mouth of the side-canon, coming down from Emmons' 

 Peak, were several hundred feet of bluish-gray calcareous and siliceous 

 shales. At the point where tlie cafion bends again to the northward, the 

 first outcrops of the Weber Quartzite were recognized, dipping about 2.0°. 

 The same general series in these beds was found as elsewhere, namely, 

 striped sandstones above, next purple quartzites with clay beds, becoming 

 lighter-colored and more compact toward the base. Where the dip of these 

 beds shallows to 10°, the same canon-within-canon structure, already noticed, 

 is found, "though less developed than on the Ute Fork. 



The gateway of the western branch is more pronounced, the Triassic 

 sandstones forming a narrow transverse ridge, enclosing the broad open 

 valley above, which is some 15 miles in length. Some clayey beds above 

 the sandstones were supposed to belong to the Jurassic formation. From 

 1,500 to 2,000 feet of Triassic sandstones are exposed in section here, dip- 

 ping from 30° to 35° south, with a strike of north 65° to 75° east ; their 

 upper part is formed by about 500 feet of massive, cross-bedded, white sand- 

 stones, underlaid by a series of white and buff beds grading off into red 

 sandstones, whose color becomes deeper as one descends. The broad val- 



