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LEWIS G. WESTGATE 



glacial date at a height of 12,800 feet above sea-level. The steep slope 

 on the left is the upper edge of Boswell Gulch amphitheater, and is 

 of glacial origin, and the view shows the manner in which cirque- 

 action was gnawing into the preglacial topography at the close of the 

 last glacial period. 



In using the present topography of the non-glaciated areas about 



Fig. 14.— La Plata Peak from the north side of Lake Creek. 



the Upper Arkansas to illustrate the preglacial topography, it is 

 assumed that substantially no change has taken place in those areas 

 since the commencement of glacial time. Strictly this is not true, 

 as these areas were subjected to subaerial erosion during Pleistocene 

 and post-Pleistocene times; but it is not believed that the kind of 

 changes then going on was different from the changes of preglacial 

 time. Nor does it seem probable that the amount of change which 

 has taken place since the commencement of the Pleistocene would 

 be great for an area which had then reached maturity under atmos- 

 pheric and stream agencies. 



