48 UNIVERSITY OF COLORADO STUDIES 



ii,ooo feet, and in many places they did not extend much below 8,000 

 feet, though some are known to have reached about 6,000 feet. In 

 length they ranged from less than a mile to over 70 miles and usually 

 reached a depth of 500 to 600 feet, though numbers reached 1,000 

 feet, a few 1,500 feet, and some even more. 



Characteristic Features of the Glaciated Area. — The glaciers 

 occupied the upper portions of canyons and valleys, which now abound 

 in such evidence of the former action of ice as U-shaped valleys (to 

 the exclusion of V-shaped), moraines, cirques, transverse terraces, 

 roches moutonnees, polished, fluted and striated surfaces, etc. 



Economic Relations 



All who are familiar with glacial phenomena are aware that glacial 

 geology has considerable economic importance. This has long been 

 recognized in the area covered by the great Continental Glacier. 

 It is equally true in our mountains. In various parts of Colorado, 

 glacial gravels have been worked as placer claims.^ As will be seen 

 by examining the locaHties reported upon, many of the important 

 metal mining districts are partly covered by glacial debris, which may 

 cover valuable ore deposits and thus prevent prospecting or make 

 exploration less profitable. Miners unfamiliar with glacial phenomena 

 have often found "float" upon the surface of moraines which came 

 from miles away, and have wasted much time and money in sink- 

 ing shafts or running tunnels in the hope of disclosing the veins from 

 which the ore came. In other cases attempts have been made to dig 

 through moraines of great depth for bedrock upon which to place 

 reservoir dams for irrigation and power purposes, in the supposition 

 that they were thin, superficial deposits of stream-laid materials. 



Most of the natural lakes of our upper mountain valleys which are 

 now being used for storage of water for irrigation, power or domestic 

 use, are glacial lakes, and they form one of Colorado's greatest assets. 



■ Enduch, F. M., "Report upon the Geology of the San Luis District," Seventh Ann. Kept. U.S. Geol. 

 and Geog. Sun. Terr., for 1873, p. 347, 1874; Stevenson, John J., " Geology of a Portion of Colorado Explored 

 and Surveyed in 1873," Geog. and Geol. Explor. and Sure. W. of loolh Meridian, Vol. Ill, p. 431, 1875; Lakes, 

 Arthur, "Glacial Placer Beds on the Flanks of the Mosquito Range, South Park, Co\or?iAo," Mines and 

 Minerals, Vol. XXII, p. 469, 1902; SALiSBtmY, Rollin D., "Glacial Work in the Western Mountains in 

 1901," Journ. Geol., Vol. IX, p. 731, 1901; Capps, S. R., Pleistocene Geology 0/ the Leadville Quadrangle, Colo- 

 rado, U.S. Geol. Surv., Bull. No. 386, p. 15, 1909. 



