BULLETIN OF THE GEOLOGICAL SOCIETY OF AMERICA 



VOL. 17, PP. 251-274, PLS. 25-31 JUNE 22, 1906 



GLACIAL PHENOMENA OF THE SAX JUAN MOUNTAINS, 



COLOEADO * 



BY ERNEST HOWE AND WHITMAN CROSS 



(Presented by title before the Society December 2S, 1905) 



CONTEXTS 



Page 



Introduction 251 



The last stage of glaciation 252 



Character and extent 252 



Terminal moraines of the last stage 254 



Lateral moraines 256 



Valley train 258 



Time of recent glaciation 259 



Occurrence of drift older than the last stage of glaciation 260 



General character and distribution of the drift material 260 



Region in which the old drift occurs 260 



The deposits of earlier drift , . 261 



Origin of the drift 263 



Early terrace gravels of Cow creek 266 



Interglacial erosion 267 



Gravel -covered terraces of the lower Animas and San Juan rivers 268 



Comparison with similar deposits elsewhere in the Rocky Mountain 



province 271 



Summary 272 



Description of plates 273 



Introduction 



For the last ten years, during which the survey of the San Juan region 

 of Colorado has been in progress, evidence has been accumulating showing 

 that in all probability the mountains have been subject to more than one 

 period of glaciation during Pleistocene time. The fact of more than one 

 stage of glaciation in the Rocky Mountain region was established by 

 Salisbury and Blackwelderf in 1902 through observations made in the 



* Published by permission of the Director of the U. S. Geological Survey, 

 t R. D. Salisbury and Eliot Blackwelder : Glaciation in the Bighorn mountains. 

 Journal of Geology, vol. xi. 1903, pp. 216-223. 



XXI — Bull. Geol. Soc. Am., Vol. 17. 1905 (251) 



