144 GEOGRAPHIC DISTRIBUTION. 



A good section can be obtained by passing- over the 6-wi-yu-kuts 

 plateau. On the northeast, this plateau culminates in a high ridge of cherty 

 and brecciated limestone which is the base of the Red Wall Group. By 

 starting at the eastern extremity and foot of this ridge and going southwest- 

 ward across the plateau and descending into Brown's Park until the axis ol 

 the flexure is reached, you pass over the upturned edges of the Uinta Sand- 

 stone. This section gives a thickness to the beds of more than 13,000 feet. 

 The factors used in the measurement were the distance between the extrem- 

 ities of the line along which the section was made as determined by the 

 topographers, and the observed dips along the line at subequal distances 

 of about 200 yards. In 1871 we attempted to make a section from the axis, 

 through the Canon of Lodore, but the difficulty of navigating the river was 

 so great that we could not perform the task with satisfaction; but the thick- 

 ness of the beds found along this line was not less than 13,000 feet. 



The Uinta Sandstone crops out along the base of the wall through the 

 upper part of Whirlpool Canon. On the north side of the Yanupa Plateau, 

 south of the Yampa River there is a monoclinal flexure and fault by which 

 the Carboniferous rocks are uplifted several thousand feet. There are three 

 cations running across this displacement which cut through the Carbonif- 

 erous rocks and reveal in their walls several hundred feet of the upper 

 members of the Uinta Group. The anticlinal uplift which forms Junction 

 Mountain is bisected by the Yampa River. The gorge through which the 

 river runs is called Junction Mountain Canon. In the heart of the canon 

 Uinta Sandstones are seen. 



UNCONFORMITY AT THE SUMMIT OF THE UINTA GROUP. 



A period of erosion or dry land condition intervened between the deposi- 

 tion of the Uinta Sandstones and of the Carboniferous Groups, 



In Whirlpool Cm! on the red sandstones of the Uinta Group are thrust 

 up into the sandstones and shales of the Lodore Group, and in some cases 

 almost sever them; that is. the Uinta Sandstones were deeply eroded into 

 abrupt valleys with steep cliffs, some of them 400 feet high, anterior to the 

 deposition of the Lodore Group. There is a difference of dip between the 



