CERTAIN GEOGEAPIC DISTRICTS DESIGNATED. 147 



again seen. I shall call the Yampa Plateau and adjacent country, together 

 with the region embraced in the Junction Mountain uplift, the Yampa dis- 

 trict. 



ISLAND PARK DISTRICT. 



Finally, west of the lower end of the Canon of Lodore and Whirlpool 

 Canon there is a zone stretching to the westward where all these groups 

 are in like manner exposed. At the foot of Whirlpool Canon lies the beau- 

 tiful valley known as Island Park, which is embraced in this zone. I shall 

 call this the Island Park district. 



LODORE GROUP. 



This group of rocks is seen in Lodore Canon, from which locality it 

 takes its name. Here it fills valleys in the Uinta Sandstone and buries the 

 ancient cliffs and hills of the dry land period. These facts were set forth in 

 the last section. 



The group is composed of soft sandstones and shales with conglomerates 

 at the base and against the ancient hill sides. Its outcrop on the northwest 

 side of the cation is of very limited extent and is not represented on the map, 

 but on the southeast side of the canon it mounts the wall for several miles 

 and appears in Dunn's Cliff, where its thickness was measured and found to 

 be 460 feet. Its outcrop is represented on the map by a narrow line. On 

 the north side of the Uinta Mountains these rocks have been seen at but one 

 point, viz, a little west of Beehive Point, and there is some uncertainty about 

 this observation. Carboniferous fossils have been found in these beds. 



The area of the outcrop at the bottom of Whirlpool Canon is so narrow 

 that the color has not been introduced on the map in that locality. 



RED WALL GROUP. 



Extensive outcrops of the Red Wall Group are found on the flanks of 

 the Uinta Mountains. On the north side the entire group is composed 

 chiefly of limestone, many of the beds being cherty. On the south side of 

 the mountains many sandstones are intercalated with the limestone. About 

 ten miles from Flaming Gorge in a southwestely direction, these beds are 

 found dipping to the north, and as they are followed along the strike to the 



