58 UNIVERSITY OF COLORADO STUDIES 



400 feet The ice sheet overrode all the hills and valleys in 



this district If this [Roaring Fork] valley were as deep at the 



time when this great glacier existed as at present, the thickness of 

 the ice must have been at least 3,000 feet." Stone^ says the Roaring 

 Fork Middle Branch Glacier was 15 miles long, one of its moraines 

 forming the dam of Lake Ivanhoe, and glaciers from the west slope 

 of the mountains extended down Rock Creek 12 miles. 



San Juan Region. — This great mountain mass covering an immense 

 area in the southwestern part of the state, during the whole of the 

 glacial epoch, as at present, presented the first high mountains to 

 intercept the warm moist currents from the Gulf of California. Hence 

 we find here, as would be expected, abundant evidence of the former 

 action of enormous glaciers.^ 



The Las Animas Glacier is said by Stone to have been 70 miles 

 long, extending down the river beyond Durango and reaching an 

 altitude of little over 6,000 feet, with a depth at Silverton of 1,000, and 

 five miles below Silverton 1,500 feet. The upper valleys of the Los 

 Pinos, San Juan, Navajo, Chama, and probably all the other streams 

 in the area which headed at the crest of the mountains, contained 

 glaciers. According to Hills the San Juan Mountain glaciers covered 

 "nearly the whole of the habitable portion of Hinsdale, San Juan, 

 Ouray and San Miguel Counties and a large portion of the counties 



'Stone, George H., "Remarks on the Glaciation of the Rocky Mountains," U.S. Geol. Surv., Mon., 

 Vol. XXXIV, pp. 349-50, 1899. 



" Endlich, F. M., "Ancient Glaciers in Southern Colorado," Ninik Ann. Repl. U.S. Geol. and Geog. Surv, 

 Terr., for 1875, pp. 216-26, 1877; Hills, R. C., "Extinct Glaciers of the San Juan Mountains, Colorado," 

 Proc. Colo. Sci. Soc, Vol. I, pp. 39-46, 1883; Amer. Journ. Science, 3d Ser., Vol. XXVII, pp. 391-96, 1883; 

 Howe, Ernest, " Glacial Phenomena in the San Juan Mountains," Science, N.S., Vol. XXIII, pp. 306-7, 1906; 

 Land Slides in the San Juan Mountains, Colorado, U.S. Geol. Surv., Prof. Paper No. 67, 1909: Howe, Ernest, 

 and Cross, Whitman, "Glacial Phenomena in the San Juan Mountains, Colorado," Bull. Geol. Soc. Amer., 

 Vol. XVII, pp. 251-74, 1906; Cross, Whitman, and Spencer, Arthur Coe, "Description of the La Plata 

 Quadrangle," La Plata Folio, No. 60, Geologic Atlas of the United States, U.S. Geol. Surv., p. 6, 1899; Cross, 

 Whitman, and Howe, Ernest, " Geography and General Geology of the Quadrangle," Silverton, Folio No. 120, 

 Geologic Alias of the United States, U.S. Geol. Surv., p. 20, 1905; "Topography and Geology," Needle Mountairt 

 Folio, No. 131, Geologic Atlas of the United States, U.S. Geol. Surv., pp. 1-12, 1905; "Geography and General 

 Geology of the Quadrangle," Ouray Folio, No. is3. Geologic Atlas of the United States, U.S. Geol. Surv., pp. 7-15, 

 1907; Cross, Whitman, "General Geology," Telluride Folio, No. 57, Geologic Atlas of the United States, U.S. 

 Geol. Surv., pp. 9-15, 1899; Spencer, Arthur Coe, "Erosion of the Rico Dome and Recent Geologic His- 

 tory," Twenty-first Ann. Rept. U.S. Geol. Surv., for 1899-1900, Part II, p. 159, 1900; Salisbury, Rollin D., 

 "Glacial Work in the Western Mountains in 1901," Journ. Geol., Vol. IX, p. 731, 1901; Stone, George H., 

 "Remarks on the Glaciation of the Rocky Mountains," U.S. Geol. Surv., Mon., Vol. XXXIV, pp. 338-45, 

 1889; "The Las Animas Glacier," Journ. Geol., Vol. I, pp. 471-75, 1893. 



