GEOLOGICAL SURVEY, OF THE TERRITORIES. 63 



crosses Green River to the southeast, though interrupted from time to 

 time by portions swept away, is plainly a portion of what we have called 

 Photograph Ridge all along the northern slope of the Uintas. The dif- 

 ference in the texture of the carboniferous rocks on Green River, and 

 those forming the high ridges on Black's Fork and Bear River, indicates 

 that the latter were partially changed by heat. The lofty triassic ridge 

 facing Green River, from which we take this extended vieAV, reaches off 

 to the south of west, about fifteen miles, in full size, when it is broken 

 into fragments and disappears on the surface. In descending the valley 

 of Henry's Fork, we noticed a high fragment of a ridge to the south, 

 rising about two thousand feet above the bed of the creek, which seems 

 to have been cut off from the north side of Photograph Ridge, but is 

 now so covered with drift that no sign of the basis rocks can be 

 detected. The upper portion is covered with a belt of dense pines, and 

 the remainder is smoothed down and covered with a good growth of 

 grass. It is a beautiful ridge to the eye, without a sharp or angular 

 point. I have no doubt that its nucleus is triassic. It is about fif- 

 teen miles in length, and breaks off quite abruptly, when the well- 

 defined triassic ridge commences and continues in a somewhat tor- 

 tuous line across Green River near the mouth of Henry's Fork. The 

 only other indications of this ridge are the rather faint traces of it on 

 Black's Fork and Bear River. The Jurassic and cretaceous ridges 

 extend westward only five to ten miles, and disappear, not to be 

 seen again until we reach Bear River and beyond. Intermediate be- 

 tween the lower cretaceous ridges and the lower tertiary beds is a 

 broad, open, valley-like space, three to five miles wide, which is occupied 

 by yellow and brown indurated clays. This valley-like space extends 

 from the base of the Uinta Mountains, across Henry's Fork near its 

 mouth, and over Green River in a southwest and northeast direction. 



It would appear to have been a valley of denudation from forces hav- 

 ing their origin in the Uintas. In this interval are numerous fragments 

 of ridges which must have been once continuous, and which are now 

 left to show the vast amount of rocky material which has been swept 

 away. Over the surface is a considerable thickness of drift, composed 

 of the well-worn boulders of sandstones, quartzites, and limestones 

 which undoubtedly came from the Uintas. Still farther to the west, are 

 the full series of miocene and tertiary beds, not less than three thousand 

 to five thousand feet in thickness, extending to Fort Bridger and beyond. 



If we were to extend this tremendous development of the geological 

 formations from the quartzites to the tertiaries, as shown at Green River, 

 where they appear to have suffered comparatively little erosion, all along 

 the northern slope of the Uintas, far west to the Wasatch range, we 

 should be doubtless reconstructing the former conditions of the surface ; 

 and we may thus form a dim conception of the tremendous erosive forces 

 which have operated in this region. We may thus account for the vast 

 thickness of drift and immense quantities of stray boulders which are 

 scattered over the sides and foot-hills of the mountains far out into the 

 plains. The further these worn rocks are found from the mountains, the 

 smaller and more rounded they are, at once revealing the source from 

 whence they came. 



On the morning of October 8 we left our camp at the mouth of Henry's 

 Fork taking a small pack-train for a three days' trip down the Green 

 River to Brown's Hole. Crossing Green River we followed an Indian 

 trail, which led us over the high ridge that forms the northern 

 wall of the broad valley or hole at the junction of Henry's Fork with 

 Green River. The general course of the ridge for the first thirty miles 



