GLACIATION IN THE TELLURIDE QUADRANGLE 515 
mesa at an elevation of 9,000 feet, or about 1,000 feet above the 
stream. This drift consists of a narrow, thin sheet of glacial débris, 
with bowlders of granite and diorite-monzonite, some of them 
striated, mingled with a much larger number of sandstone bowlders 
and fragments which cannot be distinguished from the Dakota 
sandstone, which here forms the bed rock. Opposite the mouth ot 
Lake Fork the drift is found farther north, covering an area which 
suggests a lobelike expansion of the border of the ice up the valley 
of the small tributary which enters from the north, and over the low 
divide northwestward into the upper part of the valley of a tributary 
of Deep Creek. At the point on the eastern side of the lobelike 
expansion, where the boundary of the drift returns to the edge of 
the canyon, a well-marked morainal ridge occurs. It has a length 
of about 20 rods, a height in some places of as much as 30 feet, and 
contains bowlders in variety up to five feet in diameter, some of 
them showing striations. Eastward from this morainal ridge the 
boundary of the drift leaves the top of the mesa, descending rapidly 
some 300 feet over the still steep canyon wall toward the conspicu- 
ous moraines which partially fill the valley of the San Miguel in the 
vicinity of Keystone. 
The moraines below Keystone are formed from material brought 
partly by ice advancing down Lake Fork, partly by that coming 
down the main valley from the east. San Juan bowlders up to 15 
feet or more in diameter characterize the drift from the east; 
granite or diorite-monzonite in bowlders up to about 3 feet in 
diameter, that from the south. The mesa lying in the angle between 
the main valley and Lake Fork is covered with drift brought 
from the south; this drift extends eastward more than half a 
mile from the nearly perpendicular rock face which at this point 
forms the upper part of the east wall of the canyon of Lake Fork. 
While there is more or less commingling of drift from the two sources, 
yet, speaking generally, the small tributary of the San Miguel River, 
which enters from the south about one mile east of Lake Fork is the 
dividing line between drift from the east and from the south. 
Half a mile west of this tributary and between the railroad and the 
San Miguel River, the moraines take the form of low ridges extend- 
ing in a northeast-southwesterly direction. On the north side of the 
