Mented by large additions of glacial material from the Need 
hk. C. Hills—Extinet Glaciers of Colorado. 393 
River region bowlders of quite large size, usually granite, are 
distributed over the country five miles west of the town of 
Durango and nearly sixty miles from the source of the Animas 
River. No rocks are exposed in the vicinity older than the 
Colorado Cretaceous, and the nearest exposure of granite is at 
Elbert, eighteen miles up-the river. 
In the Rio San Miguel region the ice moved westward with 
the general course of the San Miguel River, and crossed diago- 
nally the course of the south branch of that stream. To what 
distance it extended I am unable to say, but I have observed 
erratic bowlders of eruptive rock on the mesas flanking the 
an Miguel, thirty-five miles from the source of the river. 
this area is marked by a Jong ridge of Archean rocks running 
diagonally from the Cimarron southwesterly to the Uncom- 
pahgre Valley and known as the Vernal Mesa. Consequently, 
the greatest extension of drift is toward the latter, where 
try lying between the Cimarron and the mouth of Indian Creek 
on the Lake Fork of the Gunnison. 
As the ice sheet retreated it became divided and finally sep- 
arated into distinct glaciers corresponding to the principal val- 
leys. Of these the Animas glacier was probably the largest. 
Tt formed the beautiful and fertile Animas Park in La Plata 
County and Baker’s Park in San Juan county. It was aug: 
e 
and Cascade Mountains, and a short distance above Elbert was 
probably at one time nearly three miles wide. Between Elbert 
and Silverton the rounded surfaces of the crystalline schists 
oye glacial scratches 1200 to 1500 feet above the old glacier 
bed. 
- ‘Two parallel terminal moraines cross the lower end of 
Animas Park at Animas City. There is a moraine at the 
lower, and another at the upper end of Baker's Park. 
__-Yext in importance was probably the Hinsdale glacier, oceu- 
ting the upper valley of the Lake Fork of the Gunnison. It 
ormed the basin of Lake San Cristobal, and, as shown by the 
adrift covering the low hills northeast of Lake City, was at one 
“me nearly a mile wide. Lake City is about twenty-four miles 
from the source of the river and about fifteen miles from the 
s 
