254 HOWE & CROSS GLACIAL PHENOMENA, SAN JUAN MOUNTAINS 



mediate between the proximal and distal extremities of the valley glaciers, 

 corrie or cliff glaciers occurred, some of which, together with those in the 

 more sheltered cirques, continued to exist until very recent times. 

 Evidence for this is found in the great freshness of their small moraines 

 and the bareness of the cirque floors. In fact, ice was seen by Cross in 

 1895 in the large cirque called "The Great Amphitheater" on the Hayden 

 map, which lies west of Mount Sneffels, at the head of a fork of Dallas 

 creek. The ice occurred at the base of the high precipitous southern wall 

 of the basin, a little east of Dallas peak. Although the ice had the ap- 

 pearance of a great snowbank, it was crevassed and of a characteristic 

 green color. 



The extent of the glaciers occupying such large valleys as the Animas 

 and Uncompahgre is well shown by their terminal moraines, which lie 

 just within the zone of foothills bordering the higher mountains. No 

 glaciers belonging to this last stage extended as far as the region of low 

 relief generally known as the plateau country. The length of the Animas 

 glacier was nearly 50 miles, of the Uncompahgre not more than 18 or 20. 

 The absence of all terminal moraines in the foothill zone and the relative 

 abundance of drift higher up many of the somewhat smaller valleys would 

 seem to indicate that they contained ice streams that never extended 

 beyond the region of the higher mountains. The Vallecito glacier, which 

 occupied the valley of that name, joining Pine river in the southern foot- 

 hills, belonged to this class, more characteristic of the south than the 

 north side of the San Juan. 



TERMINAL MORAINES OF THE LAST STAGE 



Through the borderland of the San Juan an abundance of drift testifies 

 to the extensive glaciation to which the region has been subjected. A 

 great part of this drift is relatively youthful, as shown by the fresh con- 

 dition of the boulders and the insignificant modification to which the form 

 of the morainal deposits has been subjected. 



The great terminal moraine of the Uncompahgre glacier crosses the 

 valley just south of the point where Dallas creek enters and close to the 

 town of Eidgway, about 18 miles from the head of the river (figure 2) ; 

 it is 400 feet high in places and more than 2 miles long, with an average 

 width of one mile; it has relatively steep upstream faces and gentler 

 slopes down stream. Its surface is uneven and hummocked and contains 

 numerous depressions or kettle-holes. The moraine is cut through about 

 in the middle by the Uncompahgre river, and exposures along the stream 

 show the typical morainal character of the material, which consists of 

 subangular and striated boulders and unstratified gravel and fine sand, 



