BRIDGER'S PASS EEGION. 157 



to the Fox Hill group, at the base of which are found exposed a few beds 

 of bluish clays, representing the upper line of the Colorado Cretaceous. 



Bridger's Pass, which connects the valleys of the Upper Sage Creek and 

 the South Fork of the Little Muddy, has been eroded out of the soft beds 

 of the Colorado Cretaceous. Along the northern and western borders of 

 this valley extends a ridge of white massive sandstones of the Fox Hill 

 group, standing at angles of 10° to 25°, and curving in strike approxi- 

 mately with the shape of the ridge. At the gap in the ridge, just below 

 the forks of the Little Muddy, through which the stage-road passes, these 

 sandstones have a strike due north and south, with a dip of 15" to the west- 

 ward. To the south of the gap, they may be traced for some distance along 

 the eastern face of the bluffs, and then disappear under the conglomerates 

 which form the surface of the plateau. To the north, with a strike bending 

 to the eastward, they form a continuous ridge about 15 miles in length, 

 showing a bluff face to the southwest toward Bridger's Pass, at the base of 

 which are exposed the clayey beds of the Colorado group. A thickness of 

 3,000 to 4,000 feet of heavy-bedded sandstones, mostly white and buff, with 

 a few included beds of shale and some thin seams of coal, dipping to the 

 northwest at an angle of 10° to 20°, are here exposed. 



The flat-topped summit of this ridge, above Bridger's Pass, is covered 

 by pebbles and boulders of micaceous gneiss and granite, with smaller peb- 

 bles of pure white quartz, which originate evidently in the Archaean beds 

 exposed at the northern point of the Park Eange. These result from the 

 decomposition of the Wyoming Conglomerate, of which a thickness of about 

 40 feet is still found on the more sheltered portions of the ridge, where it 

 consists of small pebbles about the size of a hazel-nut, of quartzite and crys- 

 talline rocks in a white calcareous matrix. 



The higher beds along the northwest sloj^es of this ridge belong to the 

 'Laramie Cretaceous. As seen on the flanks of Separation Peak, they con- 

 sist largely of sandstones of rusty colors, carrying considerable iron, and 

 showing several coal-seams. One bed in particular is of so bright a red 

 color that it might almost be mistaken for one of the Red Beds of the 

 Triassic; it is, however, of generally finer grain, and is more thinly laminated. 



The shallow valley skirting this ridge on the northwest, through which 



