520 ALLEN DAVID HOLE 
stream crosses the lower ridge of the moraine, exposing unassorted 
glacial drift with bowlders in variety, ranging in size for the San 
Juan bowlders up to nearly 20 feet in diameter; the depth of the 
cut is here about 50 feet. Where the stream crosses the higher 
ridge of the moraine the cut is comparatively broad, and about 150 
feet deep. The area south of the moraine at this point shows some 
effects of ponded waters; the topography, however, is not such as 
is due to the silting-up of a lake; it is rather that of a flood-plain 
which has been somewhat eroded. 
West of Prospect Creek gap the topography is not so simple as 
to the east. The lower ridge persists, but the higher one flattens 
out southward into a series of gentle swells, and finally joins a higher 
point west of the road which leads from Keystone up to the plateau 
to the southeast. This arrangement of the drift, together with the 
sharp turn that Prospect Creek makes to the northward just at the 
gap, indicates that the valley of Prospect Creek extended on to the 
northwest in pre-glacial time, joining the valley of the San Miguel 
River probably somewhere near Keystone. 
Lateral moraines along the San Miguel valley—north side—The 
most easterly point at which the lateral moraine is to be found on 
the north side of the valley is on the west side of Royal Gulch at an 
elevation of about 10,000 feet. The cut made by the road at this 
point has exposed a heterogeneous mixture of clay and bowlders, 
the latter chiefly from the San Juan and Telluride formations; 
some of the bowlders are striated. The amount of this deposit is 
comparatively small; that part deserving mention as decidedly 
morainic is included within a distance of less than 4o rods along the 
side of the valley. 
Farther west, a short ridge of glacial drift occurs on the east side 
of Cornet Creek at an elevation of 9,800 feet, and on the east side of 
Butcher Creek at 9,650 feet, extending in each case from the 
eastern side of the valley to the stream channel, and rising 50 to 
6o feet higher than the somewhat flattened area just to the north. 
At the junction of the valley of Mill Creek with the San Miguel, 
no morainic ridge appears such as is found in the valleys of Cornet 
Creek and Butcher Creek. The ice from Mill Creek basin evi- 
dently had sufficient force to push out into the valley of the San 
