THE 



JOURNAL OF GEOLOGY 



MAY-JUNE, 1905 



THE TWIN LAKES GLACIATED AREA, COLORADO 1 



LEWIS G. WESTGATE 



OUTLINE 



Preglacial Topography of the Upper Arkansas. 

 Glacial Features oe the Twin Lakes Region. 

 I. Morainic System of Lake Glacier. 

 II. Pleistocene History of the Upper Arkansas. 

 III. Glacial Erosion. 

 Postglacial Changes. 

 Mountain Form. 



The Upper Arkansas occupies a broad north-and-south valley 

 between the Park Range on the east and the Sawatch Range on the 

 west. Twin Lakes are on the lower course of Lake Creek, which 

 heads in the Sawatch and flows east to the Arkansas. The lakes are 

 held back by two small recessional moraines deposited by the glacier 



1 The writer, on returning from the Harvard excursion to the Great Basin in 1904, 

 spent several weeks in the valley of Lake Creek. Together with Professor W. M. 

 Davis, he had stopped here for a few days earlier in the summer, and he wishes to 

 express his indebtedness to Professor Davis for pointing out the district to his attention 

 as deserving study for its glacial features, and for suggestions in the field and later. 



The only early detailed report on the region is found in the Annual Reports of the 

 Hayden Survey for 1869, 1873, and 1874. A paper by Capps and Leffingwell, which 

 was published in the Journal of Geology for November-December, 1904, discusses the 

 glacial geology of the upper Arkansas valley, and with the conclusions of these writers 

 the author is in substantial agreement, in so far as the two papers deal with the same 

 area. Professor Davis, in Appalachia, November, 1904, uses the valley of Lake 

 Creek to illustrate glacial erosion. 1 



Vol. XIII, No. 4 285 



