350 E. B. BRANSON BULL LAKE CREEK ROCK SLIDE 



flows ill a granite canyon 2,000 feet deep nearly two miles from the cliff, 

 and the creek has not been near the cliff since it began cutting into gran- 

 ite;. A normal erosion history would liave given a largo talus slope at the 

 base of t\w cliff and the clilT M'ould have been reduced to slopes during 

 the time nccessaiy for exca\ating the inner canyon, but there is little or 

 no tahis at the base of tlie cliif next the slide. The valley has been gla- 

 ciated, hut tile glacier seems not to have a])proaclied the north clifF near 

 enough to interfere with the slide or to have distnr1)cd talus if it had been 

 ]u-esent. East of tlic slide talus has accumulated to half the height of the 

 clifl', although the stream is much nearer than it is in the slide region. 

 The evidence seems to proAT> that the rock slide has removed the great 

 masses of i"ock that slumped o(f, while the cliff retreated more than half a 

 mile. 



Other Slides in the Wind Ejvee Mountains 



Eock slides occur on . a small scale in several deep valleys in the Wind 

 Eiver Mountains, but they are high and far back in the mountains and 

 have escaped observation. Blackwelder^ mentions. the ^^general absence 

 of earthflows from such ranges as the Wind Eiver Mountains," but in a 

 later paper he says : 



"In a few cirques, talus glaciers, such as those described by Cross and Howe 

 in the San Juan Mountains of Colorado, have been formed. On the northeast 

 side of Sheep Mountains, at tlie northwest end of the Wind River Range, there 

 is a good example showing the tongue-like form and surface corrugations." * 



On the north side of Big I*opo Agie Eiver, 12 miles from Lander. 

 Wvoming, a slide of large size was once active, but seems to have been 

 (piiet for more than 20 years, as a road huilt across it more than 20 years 

 ago has not been disturbed. On the south side of the same stream a cliff 

 about one mile long has develo])e(l l)y slumping, caused by the movement 

 of the slippery Bull Lake ('reek sliales. On the south side of Tjittle Popo 

 Agie Eiver, about 21 miles from Lander and opposite the mouth of North 

 Fork, there is a slide similar to the one on the south side of Big Popo 

 Agie. In all of the examples mentioned the active agent of movement is 

 the Bull Lake Creek shale. 



■' Rnll. Oeol. Soc. Am., vol. 23, p. 401. 



^ .Tom-, of (Jeol., vol. 2:?, 1915, pp. 3:M-3:{5. 



