UPPER ARKANSAS VALLEY. 345 



in height. The moraines have been deeply cut by the river. I have not 

 been able to find any moi'aiues below Dallas, and probably these moraines 

 between Ridgway and Dallas mark the extreme advance of the ice. 



The bottom of the valley from Onray northward 40 miles to beyond 

 Montrose is covered with rounded and rolled gravel and coarser matter. 

 In places this overwash sheet is more than a mile wide. The fact that the 

 same sort of gravel plain extends for 12 miles above the outermost moraines, 

 proves that the subglacial streams during the retreat for a long time contin- 

 ued to pour out glacial gravel into the open valley in front of the ice. 

 Where observed this gravel is rather horizontally stratified and shows none 

 of the appearance of the reticulated kame ridges. The retreat of the ice 

 appears to have been rather gradual, since there are only small retreatal 

 moraines in the lower parts of the valley. The sides of the main valley 

 show a sprinkling of erratics, except where precipitous. 



The Uncompahgre glacier reached only 8 miles beyond the mountains, 

 but transported a very large amount of morainal matter, and also glacial 

 sediments. The base of the terminal moraine at Ridgway is at 7,000 feet 

 elevation. 



There were numerous glaciers in the valleys tributary to the Gunnison 

 River, some of them of larg-e size. 



UPPER ARKANSAS VALLEY. 



The glacial deposits of this valley were first described by the Haydert 

 Survey, and later by Emmons in his Leadville monograph.^ It is impos- 

 sible to do justice to this interesting valley without going into detail more 

 than is here practicable, and only a few points will be noted. The first 

 thing that attracts attention is the enormous size of the moraines which the 

 glaciers that originated in the Sawatch Range have left across the main 

 valley. The Arkansas Valley from Leadville southward to Salida is from 

 2 to 4 miles wide between the bases of the steep mountains. The lateral 

 glaciers flowing down from the mountains did not fill this broad valley — at 

 least they did not for a long time during the last part of the ice period — 

 and thus left moraines at the sides and in front of their valleys. Some of 

 these moraines cover several square miles and are up to 1,000 feet in height. 



' Geology and Mining Industry of Leadville, with atlas, Mon. U. S. Geol. Survey, vol. 12, pp. 40-42,, 

 1886. 



