AREAL GEOLOGY OF LOWER CLEAR CREEK 265 



tuated than the topography of the eastern section. The topography of the 

 eastern portion may be defined as subdued topography, except where it is 

 deeply cut by Clear Creek and Bear Creek. 



Unlike the Georgetown and Central City Quadrangles, there is little 

 evidence of glaciation. On the flanks of Squaw Mountain, especially at 

 the head of North Beaver Creek, the amphitheater-like topography gives 

 one an impression of a glacial cirque, and the idea receives confirmation by 

 an accumulation of detrital material just at the beginning of the V-shaped 

 valley of North Beaver Creek. To a less extent South Beaver Creek 

 exhibits the same phe- 

 nomena, and both 

 creeks continue their 

 courses as V-valleys. 

 The subdued topog- 

 raphy of the eastern 

 portion strongly re- 

 minds one of a pene- 

 plain, and there is 

 good reason to con- 

 sider that all the east- 

 ern portion was once ' w • . ■ ^^ 

 base leveled, and Fig. 2. 

 since has been deeply dissected on the north and south by Clear Creek 

 and Bear Creek, and their respective tributaries. 



This peneplain or base-level was elevated in common with the re- 

 mainder of the Rocky Mountains in Tertiary times, and Clear Creek and 

 Bear Creek canons with the canons of their tributaries have been entirely 

 eroded since that period. In many cases the side streams have not yet 

 cut deep canons, and we have at their sources the gentle, well-rounded 

 slopes of Tertiary time, in sharp contrast with the deep canons of the 

 lower portions of the same streams. This is true also of the upper waters 

 of Clear Creek and Bear Creek outside of the area here considered. In 

 fact, a very close approximation to Tertiary topography could probably 

 be reached in a topographic map of the eastern portion of the area under 

 consideration by simply neglecting the deep canons and putting in their 



