GLACIATION IN THE TELLURIDE QUADRANGLE Feu 
In this connection it should be noted that not all the valleys 
tributary to valleys which were occupied by glaciers are hanging 
valleys. For a given stream it may occur that part of the tribu- 
taries occupy hanging valleys, while a part are in topographic 
adjustment with the main stream. For example, east of the city 
of Telluride the San Miguel River receives tributaries from glaciated 
valleys as follows: Bear Creek, Deertrail Creek, Bridal Veil Creek, 
Ingram Creek, and Marshall Creek. Of these, Deertrail basin, 
Bridal Veil basin, and Ingram basin are hanging valleys, while 
Bear Creek valley and Marshall basin cannot be so classed. Of the 
two larger tributaries from the south, Bridal Veil Creek enters the 
cirquelike head of the San Miguel valley by a sheer fall of 350 feet 
and with a steep grade below for another 500 feet of fall before it 
reaches the more level part of the bottom of the valley; while Bear 
Creek, two miles farther west, draining a glaciated area less than 
that of Bridal Veil basin, enters the San Miguel River by a grade 
no steeper than is usual for mountain streams. Other things being 
equal, it would seem that a valley draining a small area would be 
deepened less by glacial action than one draining a larger area; and 
‘if so, then the smaller valley would be more likely to be left as a 
hanging valley. However, Bear Creek valley, the smaller one in 
this instance, is not a hanging valley, while Bridal Veil basin, the 
larger one, is; some modifying conditions have therefore evidently 
been present. 
A modifying condition in this case may be (1) the difference in 
kind of rock forming the bottoms of the valleys. In Bridal Veil 
basin the San Juan formation is the underlying rock, while in the 
larger part of the valley of Bear Creek the more easily eroded 
sedimentary rocks of the Jura-Trias period outcrop in the bottom 
for two miles or more. Or the modifying condition may be con- 
ceived to be (2) a difference in the pre-glacial topography. If the 
grade of Bear Creek in pre-glacial time was not steep in its lower 
course, and if the downward cutting of the ice in the San Miguel 
valley was but little different in rate from that in Bear Creek valley, 
a hanging valley would not be formed. And on the other hand, a 
steep gradient in Bridal Veil Creek in pre-glacial time would, accord- 
ing to the principles already referred to in the case of Deertrail 
