490 E. BLACK WELDER THE GROS VENTRE SLIDfi 



irregular domes fretted with open crevasses, many of which were several 

 feet wide. By its advance the glacier-like mass gradually obstructed the 

 Gros Ventre Eiver, which soon formed a lake more than a mile in length 

 and several hundred yards in width. This still exists, but the rapid cut- 

 ting down of the outlet has already (August, 1911) lowered the surface 

 of the water about 10 feet. 



So far as observed, the motion of the slide was not at any time rapid 

 enough to be actually seen. The evidence of it, however, was plain 

 enough. It was found impossible to keep the Forest Service telephone 

 line in repair more than a few days, for the poles would slowly move 

 down hill or be overturned and thus snap the wire. The wagon road 

 soon became so hopelessly twisted and broken that it was almost impos- 

 sible for wagons to follow it without capsizing, and it was no easy task to 

 cross it even on a saddle horse. Attempts to repair the damage were 

 almost futile, because in a few days the road would be rendered again 

 impassable by folds of earth several yards in height or by gaping cre- 

 vasses with vertical walls. In a short time the old road was completely 

 destroyed, so that even traces of it are now hard to find. It thus became 

 necessary for every one who attempted to cross the slide to pick out his 

 own course, and not infrequently he was obliged to spend some hours 

 with pick and shovel grading some of the worse places- in order to render 

 it possible to take a wagon over the slide at all. 



According to members of the United States Forest Service, the slide 

 did not move as one mass, but rather in sections ; the disturbance began 

 on the east side and manifested itself week by week at new places. 

 Changes progressed most rapidly in the wet spring months and declined 

 noticeably toward autumn. The slow but apparently incessant movement 

 continued through the 3^ears 1908, 1909, and 1910, but in 1911 had prac- 

 tically ceased. 



Present Characteristics of the Slide 



As seen in 1911, the slide was a long glacier-like tongue of unassorted 

 clay and coarser debris (see plate 31), much like till except for the 

 absence of striated boulders, lining the bottom of a tributary gulch and 

 spreading out at its lower end near the Gros Ventre Eiver. At the head 

 of the gulch the slopes are relatively steep and are seamed with parallel 

 crevasses, along the lower sides of which the material has slumped down 

 in waving belts. This oversteepening of the walls at the head of the 

 valley suggests the cirque at the head of a mountain glacier. Like a 

 glacier, also, the earth-flow thickens down the valley. Furthermore, in 



