542 REPORT UNITED STATES GEOLOGICAL SURVEY. 



north, and is the route of a broad and well worn Indian trail which fol- 

 lows up Marsh Creek. The ascent is very gradual to the rim of a small 

 basin in which McDougal Creek heads. This is at the eastern base of 

 the range. The descent from the head of Marsh Creek to the- head of 

 McDougal's Creek is very abrupt, and the latter stream has a rapid de- 

 scent through a narrow and rough canon. Gray laminated sandstones 

 dipping to the westward at an angle of 20° are first crossed. These 

 abut against the edges of limestones, which also dip to the westward. 

 The angle of inclination in the limestones at first is 10°, but this in- 

 creases to 25° as we go down the canon. Eeaching a creek coming from 

 the north a few miles west of the Pass we find beds flattening out until 

 we soon cross a gentle synclinal and shortly afterwards an anticlinal 

 fold. This latter fold is continuous along the western side of the range. 

 The creek already mentioned as coming into McDougal's Creek from the 

 north cuts the range into two ridges that are parallel to each other. The 

 eastern or outside ridge is composed entirely of limestones and quartz- 

 ites of Carboniferous and perhaps Silurian age. The western ridge con- 

 tinues the main crest northward, while the eastern ends at a point east 

 of station 53. The latter was our most northern station in the range, 

 and was on limestones whose position was almost horizontal. Going 

 westward, however, this dip soon becomes 35° or 40°. To the south and 

 to the north the Bed Beds (Trias) are seen reaching up on the summits 

 of the ridge. In the valley of John Day's Biver opposite the station 

 and for some distance north of McDougal's Creek the fold of the Bed 

 Beds on the western side of the range is preserved ; but farther south 

 the fold is more abrupt and the line of sharpest folding is most eroded, 

 so that on the summit of the range we have the Bed Beds resting in al- 

 most horizontal position on the Carboniferous limestones, and in the 

 valley of John Day's Biver tbey dip 25° to 35° to the westward. Be- 

 tween these two there is a gap in which only Carboniferous shows. 

 This portion of the range, in consequence of this erosion, presents a rather 

 steep, bluffy face to the westward. The summit of the range is about a 

 mile and a half east of the valley, above which it rises nearly 4,000 feet. 

 The upper portion is an almost sheer precipice in most places. South of 

 Thompson's Pass the Absaroka Bidges continue the line of the range, 

 gradually diminishing in height towards the south. These have already 

 been considered. 



