148 GEOGKAPHIC DISTRIBUTION. 



westward they are seen to rise in a high monoclinal ridge. This ridge is 

 not well developed until we pass beyond the area embraced on the map. 

 Another outcrop is seen on the northwest corner of the 6-wi-yu-kuts Pla- 

 teau ; here the beds are standing vertically. On the eastern end of the same 

 plateau, in the Po Canon district, another outcrop appears where the beds dip 

 a little north of east in a lofty monoclinal ridge. The central mass of Junction 

 Mountain is Red Wall limestone, and the group crops out in an unbroken 

 but irregular zone along the south side of the Uinta Mountains on the east 

 side of the Canon of Lodore, in the Escalante Peaks, and on the west side of 

 the Canon of Lodore in the Island Park district. The Ti-ra-yu-kuts like 

 the Escalante Peaks are composed of the hard cherty limestones of the Red 

 Wall Group and are true flanking peaks. Here the beds all dip to the south 

 usually at a rather low angle, and along the northern margin of the outcrop 

 the cherty limestones stand in peaks. Another outcrop is seen at the bot- 

 tom of Split Mountain Canon, and, last, these limestones are exposed on the 

 Yampa Plateau on an escarpment formed by a fault or a monoclinal flexure 

 which faces the Yampa River, and which is crowned " by many towering 

 peaks. 



All these outcrops are well represented on the map. 



LOWER AUBREY GROUP. 



This group is made up of rather soft sandstones with intercalated lime- 

 stones; altogether the rocks are much more friable than the last mentioned 

 group, and they also yield much more readily to atmospheric degradation 

 than the beds of the Upper Aubrey. Where the beds of the Red Wall and 

 Upper Aubrey Groups stand in monoclinal ridges the beds of the Lower 

 Aubrey are found in the inter-ridge or valley spaces. It is seen outcropping 

 in the vicinity of Flaming Gorge and extending in a narrow zone westward 

 beyond the region embraced on the map. On the east side of the 0-wi-yu- 

 kuts Plateau its outcrop can be traced along the eastern base of the mono- 

 clinal ridge, which is composed of Red Wall limestones as described above. 

 Here the valley lies between the two monoclinal ridges and is known as Po 

 Canon. These beds are also found on both flanks of the Yampa Plateau 

 and along the southern slope of the Uinta Mountains from its eastern extrein- 



