GLACIATION IN THE TELLURIDE QUADRANGLE 513 
a typical cirque only in the fact that its walls are deeply notched by 
permanent streams (Fig. 3). 
Below this cirquelike valley head the height of the walls and the 
steepness of their slopes gradually diminish until, just above 
Keystone six miles to the westward where deposits in the form of 
moraines are abundant, the height of the walls is not more than 
Fic. 3.—Valley of the San Miguel River, elevation 9,000 feet; looking south of 
east from north side of valley. Note the flat bottom, the meandering stream, and the 
abrupt termination of the valley in the center of the view. 
400 to 600 feet with a slope not steeper, in general, than 30 to 4o 
degrees. This comparatively low elevation of the top of the valley 
walls above the stream as shown just east of Keystone is due in 
part to the fact that the San Miguel River at this point has its 
channel in glacial drift, or in the silt of a lacustrine deposit which 
fills the channel cut in the underlying bed rock to a depth of prob- 
ably 4oo feet. From the morainal deposits in the vicinity of 
Keystone to the terminus of the glaciated area near the mouth of 
