THE TWIN LAKES GLACIATED AREA 305 



One of the best illustrations of terminal facets separating non- 

 glaciated hanging valleys occurs just above the mouth of the gorge 

 on the south side of the valley. The ice here reduced the valley side 

 to an even curve leaving the wall not at all broken by rock buttresses. 

 In this manner a series of triangular facets was formed against the 

 divides between short tribu- 

 tary valleys, which right here \\ \ \ )^/s'' v\^\ // -''' 

 were not occupied by gla- v\\ C M-^s' 

 ciers. Subsequently inter- 'x' \jy't ' V / /. 

 glacial and postglacial ero- " v . / / 

 sion have cut these valleys *// / -fy' / 

 further toward the main ■ — ZjC^i^L ^^f^T'^Z ^'-^wT 

 valley floor, and have fur- 4$*^ * 



rowed the facet faces, but Fig. 9.— Truncated spur on the south wall of 



they still distinctly show Lake Creek Valle > r - 



their faceted character. The facet shows steeper in the lower three- 

 fourths of its face, a gentler, but still steep slope, above to the apex of 

 the facet. In Fig. 9 the dotted line AB marks the upper limit of 

 glaciation; the part of the facet below that line seems to represent 

 glacial abrasion, the upper part the work of glacial sapping. The 

 truncated spurs along the base of Lost Canyon Mountain have already 

 been mentioned (p. 292) while speaking of the moraine. 



Hanging valleys and truncated spurs obviously go together, and 

 hanging valleys are a characteristic feature along Lake Creek. Some 

 of these hanging valleys were occupied by glaciers, some not. Crystal 

 Lake Gulch, La Plata Gulch, and La Plata Basin are glaciated 

 hanging valleys. Willis and Boswell gulches to the east were 

 glaciated valleys, but are not hanging valleys, as the main glacier 

 did not cut below the level of the tributary valleys in this lower part 

 ■of its course. Of the three mentioned, that of Crystal Lake Gulch 

 is most characteristic. Fig. 10 shows this hanging valley as seen 

 from the opposite side of the main valley. It is a broadly opened 

 U -valley, ending on the side of the main valley about 1,000 feet 

 above Lake Creek. La Plata Basin and La Plata Gulch, the two 

 tributary valleys from the south, next west of Crystal Lake Gulch, 

 and Hayden Gulch, entering from the north opposite Crystal Lake 

 <Gulch, are hanging valleys of similar type. The other tributary 



