VALLEY OF THE UPPEE YAMPA EIVER. 185 



the few exposures that were seen indicate a synclinal fold open toward the 

 south ; the blue clays of the Colorado group, which are exposed near the 

 divide, being overlaid by heavy beds of white, fine-grained sandstones, 

 which dip to the westward, and closing around the northern point of the 

 synclinal are upturned at Bear Ridge with a steep easterly dip of 45° to 

 50"^ east. 



Bear Ridge represents an anticlinal fold, belonging to the system of 

 secondary folds approximately parallel to the trend of the main crest of 

 the mountains, which, like most of these folds, has a steeper side toward the 

 mountains, and a more gentle slope away from them In this instance, the 

 eastern member of the fold dips 45° to 50° eastward, while the western 

 beds slope at an angle of 15° to 20° westward. The axis of the anti- 

 clinal fold sinks toward the south and rises to the north, exposing the lower 

 beds at the southern point of the Whitehead Ridge, where the anticlinal 

 structure still continues, with a synclinal fold to the east between it and 

 the exposures of the Colorado clays, at the junction of Elk River and 

 Moore's Fork. The exposures of the Fox Hill Cretaceous as seen in Bear 

 Ridge show a series of massive, white, fine-grained sandstones of several 

 thousand feet in thickness. The upper beds are more thinly bedded, and 

 show some interstratified clay seams, but the beds are characteristically 

 different from the sandstones of the Laramie group. In the open country to 

 the west, where these sandstones underlie the long slopes at a gentle angle, 

 were found a few fragments of BacuUtes, which are quite characteristic of 

 this group. At the southern end of Bear Ridge, the sandstones slope off 

 more gently, bending in strike gradually round to the westward, and form- 

 ing an east and west ridge, parallel to the main elevation of the White River 

 divide, south of the limits of our map, in which the beds have a gentle north- 

 ern dip. 



The Yampa, therefore, runs approximately in the axis of a broad east 

 and west synclinal fold, in which, however, may be seen the influence of gentle 

 folds, y/hose axis runs north and south. The upper beds in this synclinal 

 valley, which consist of yellowish and buff sandstones, sometimes stained 

 red with oxide of iron; and containing considerable development of clayey 

 beds, have been referred to the horizon of the Laramie group, although no 



