THE TWIN LAKES GLACIATED AREA 287 



part of the graded rock-floor of the preglacial Arkansas. The west 

 wall of the narrow valley is granite, but the plain (AD) stretching- 

 west from its upper edge is glacial wash, and not cut on the rock. 

 The rock-plain which one naturally looks for to match that on the 

 east is buried under this wash and is shown at only one point along 

 the base of the range, just 

 south of the south Lake 

 Creek moraine, where placer 

 mining has removed the thin 



r 1 Fig. 2. — Section across the Arkansas 



cover of gravel over a con- _,. t , , _ .. 



River north 01 Granite. 



Siderable area, and shoWS a Horizontal and vertical scale, 1 inch 



graded slope of weathered =4miles (nearly) - 



granite inclining to the east, and at the same level as the back of the 

 corresponding rock-slope east of the Arkansas. Placer digging west 

 of Granite, and occasional shafts, show that the gravel is upwards of 

 50 to 75 feet in thickness; it may be much more. This gravel filling 

 is probably not thick enough to carry the bottom of the broad pre- 

 glacial valley, which ran west of the present river, down to the present 

 level of the Arkansas. The dotted line in the section restores approxi- 

 mately the surface of the preglacial valley. 



At its back edge the graded rock-slope passes into the foothills 

 of the Park and Sawatch ranges. The hillsides comprising these 

 ranges are not steep, rarely over 20°, and have graded slopes, without 

 prominent outcropping ledges, and this type of hill form is kept all 

 the way to the summits. These rise some 3,000 to 5,000 feet above 

 the valley, and are rounded and massive. Sharpened summits occur 

 only in the glaciated areas. The Sawatch Range above Granite, 

 Lost Canyon Mountain, and Mount Elbert all show this massive 

 form, which may be taken as the typical preglacial form. 



GLACIAL FEATURES OF THE TWIN LAKES REGION 



That part of the Lake Glacier (name shortened from Lake Creek 

 Glacier) which lay in the broad valley of the Arkansas was character- 

 ized by morainic deposition; that part above Twin Lakes village, 

 and which lay in the narrow valley in the Sawatch, by glacial 

 erosion. 



