EXTINCT AND EXISTING GLACIERS OF COLORADO 5 1 



of Mills's books^ is especially useful because of the accompanying 

 map which gives the location of the principal mountain peaks and 

 named ice-fields of the region north and northwest of Long's Peak. 

 This map names Hallett, Tyndall, Sprague and Andrew Glaciers. 



Extinct Glaciers of Colorado 



Age. — Colorado was not within the area covered by the Pleisto- 

 cene Continental Glacier. The Denver Basin deposits once desig- 

 nated glacio-natant drift^ and the loess are not of glacial origin. In 

 Montana the relations of deposits from the Continental ice-sheet to 

 those from mountain glaciers indicate that the latter were not earlier 

 than the Iowa epoch, and probably as late as the Wisconsin.^ In 

 Utah seven glaciers reached the shores of ancient Lake Bonneville 

 and the remains of three were partly buried on or near the shore by 

 either fluviatile or lacustrine deposits. There were at least two 

 epochs, and the latest advance was late in the history of Lake Bonne- 

 ville.'' Though the Montana, Utah, Wyoming, and Colorado glaciers 

 were likely contemporaneous, they were probably not actually con- 

 nected, owing to unfavorable intervening topography and altitudes. 

 Theoretically the same conditions would in part be required to pro- 

 duce glaciers in our mountains and to produce extensive lakes in the 

 Great Basin of the Southwest — excess of precipitation over dissi- 

 pation. Those ancient lakes had two periods of maximum exten- 

 sion, just as the mountain glaciers had. In Wyoming, also, there 

 were two glacial epochs, the latest probably of Wisconsin age or 

 later.5 



In the Leadville, San Luis and San Juan districts of Colorado, 



' Mills, Enos A., The Story of Esles Park and a Guide Book, Outdoor Life Pub. Co., Denver, 1905. 



' Emmons, S. F., "Pleistocene Geology," Geology of the Denver Basin, U.S. Geol. Surv., Mon., Vol. XXVII, 

 pp. 265-66, 274, 1896. 



3 SALiSBxmv, RoLLiN D., "Glacial Work in the Western Mountains in 1901," Journ. GeoL, Vol. IX, p. 

 720, 1901. 



•< Sallsbury, Rollin D., op. cit., pp. 725-27; Gilbert, G. K., Lake Bonneville, U.S. Geol. Surv., Mon., 

 Vol. I, p. 92, 1890; Russell, Israel C., Geological History of Lake Lahonton, a Quaternary Lake of Northwestern 

 Nevada, U.S. Geol. Surv., Mon., Vol. XI, 1885; Atwood, Wallace W., Glaciation of the Uinta and Wasatch 

 Mountains, U.S. Geol. Surv., Prof. Paper No. 61, pp. 68, 92, 1909. 



5 Salisbury, Rollin D., "Glacial Geology," Geology of the Big Horn Mountains, U.S. Geol. Surv., Prof. 

 Paper No. 51, pp. 71, 86-87, 1906. 



