GLACIATION OF THE UINTA MOUNTAINS 803 
the mountains. In the catchment basin of Provo Canyon there are 
at least forty-three lakes, and from the summit of Bald Mountain 
overlooking the area formerly covered by the ice cap seventy lakes 
may be seen. In a few cases streams are today partially ponded by 
morainic dams. In these cases the drift is not sufficiently compact 
to hold the waters until they rise and overflow, but, seeping through 
the loose deposits, the waters issue a short distance down the canyon 
as large springs. The glacial lakes vary in their longer diameters 
from a few rods to one mile and a half. Most of them, however, are 
less than half a square mile in extent. 
The hanging valleys may also be mentioned in this connection, 
for they are instances of marked changes in drainage. In this way 
scores of tributary streams have been thrown out of adjustment with 
their mains. Falls and rapids have been caused which centuries of 
work may not remove from the stream courses. 
POSTGLACIAL WORK 
Since the ice last left the Uinta Mountains, the work of weathering 
and erosion has been, with the exception of certain inner gorges on 
the south slope, trivial and insignificant. ‘The moraine material of 
the later epoch is but little disintegrated, and most of the streams are 
yet engaged in cleaning away the glacial débris from their ‘courses. 
Near the summits changes in temperature, frost, gravity, and moving 
névé, have so combined as to produce extensive talus accumulations 
about the margins of the basins. The inner rock gorges in the main 
south slope canyons are the most striking postglacial features in 
the range. On the average they are fifty to eighty feet deep and 
from five to six miles long. They are limited to the upper portions 
of the canyons, and do not appear to be due to a general rejuvenation 
of the streams. ‘They are in those portions of the canyons where the 
deepening by the ice was greatest, and therefore where the stream 
bed would be expected to be relatively low, and yet these inner rock 
gorges are distinctly below the level of ice wear and are not glaciated. 
The favorite hypothesis for the explanation of these gorges has been 
a slight postglacial uplift along an ‘east-west line about ten miles 
south of the axis of the range. 
