GLACIATION IN THE TELLURIDE QUADRANGLE 519 
to make a reservoir of the basin lying back of this ridge by filling up 
the stream-cut in the moraine; the dam thus formed has been 
largely washed away, but the name, the ‘‘Van Atta dam,” is still 
used to refer to the part remaining. Below the moraine to the 
north, are two or three secondary ridges or benches, the one most 
plainly marked being about 250 feet below the principal ridge, that 
is, at an elevation of about 9,500 feet. From these ridges glacial 
drift covers the valley slope down to the river, nearly 1,000 feet 
below; bowlders up to 8 feet in diameter occur here. 
2. A half-mile farther west another small tributary enters the 
San Miguel River from the south. The moraine here is not a well- 
marked ridge, but a level bench across the valley, showing sections 
of typical morainal débris. 
3. From the point just named westward the moraine cannot be 
distinguished for about a mile and a half. The slope of the valley 
is steep, covered with a forest of spruce and aspen, and shows 
occasional outcrops of rock in place; little glacial débris could 
remain on this slope. But at a point about one-fourth of a mile 
east of the road which leads from the village of San Miguel up the 
south slope of the San Miguel valley, glacial drift appears in 
abundance at an elevation of about 9,550 feet on the crest of the 
ridge which divides the San Miguel valley from the valley of 
Prospect Creek, and continues as a well-marked ridge from this 
point westward to the deposits near Keystone. At the point where 
the road mentioned above crosses this ridge there is a notch some 
50 feet or more in depth. Small, but distinct ridges of clay, gravel, 
and small bowlders lead off from the vicinity of this notch in a 
southwesterly direction toward the valley of a tributary of Prospect 
Creek. West of the notch referred to for half a mile or more the 
moraine consists of two distinct ridges or crests; the crests are 
never far apart, making thus a single ridge with a double crest 
rather than two separate ridges. The lower crest is always to the 
north, being from 50 to too feet lower than the other. 
Through this double-crested lateral moraine Prospect Creek has 
cut a channel sufficiently deep to allow its basin to be drained, 
though it still lacks over 350 feet of having cut down to the level of 
the San Miguel River. The sides of the cut are steep where the 
