THE PHYSIOGRAPHIC DEVELOPMENT OF THE 



BIG THOMPSON RIVER VALLEY 



IN COLORADO^ 



MARGARET BRADLEY FULLER 



Northwestern University, Evanston, Illinois 



OUTLINE 



Introduction 



Description and Classification of Units 



Pre-Wisconsin Glaciation 



History of the Units in the Big Thompson Valley 



Summary 



introduction 



The Big Thompson River rises in a snow field within a large 

 cirque on the east side of the Continental Divide in Colorado at 

 about latitude 40° 20' north. It flows in a general easterly direction 

 down the slope of the Front Range to cross the foothills and the 

 plains, joining the South Platte River east of Greeley. The por- 

 tion of the Big Thompson River under consideration may be found 

 on the Longs Peak, Mount Olympus, and Loveland quadrangles. 

 The contour interval (100 feet) is too large, however, to permit 

 map identification of many features included in this report. The 

 accompanying sketch map (Fig. 6) gives the location of the various 

 places discussed. 



The composite origin of the Big Thompson Valley may be clearly 

 shown from a study of the five distinct and successive physio- 

 graphic units which make up its course from headwaters to foothills 

 district. The separation of the different parts of the valley into 

 five areas is based upon: (i) general outline and contour of the 

 valley walls; (2) number and character of the tributary streams. 



^ Observations on the physiography of Big Thompson River Valley occupied parts 

 of the field seasons of 192 1 and 1922 while the author was engaged in a study of the 

 Pre-Cambrian geology of the Front Range in northern Colorado. 



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