Sierra and the Wahsatch Mountains were loaded with
glaciers that descended to the adjacent valleys during the last glacial
period, and that it is to this mighty host of ice streams that all the
more characteristic of the present features of these mountain ranges are
due.

But grand as is this vision delineated in these old records, this is
not all; for there is not wanting evidence of a still grander glaciation
extending over all the valleys now forming the sage plains as well
as the mountains. The basins of the main valleys alternating with the
mountain ranges, and which contained lakes during at least the closing
portion of the Ice Period, were eroded wholly, or in part, from a
general elevated tableland, by immense glaciers that flowed north
and south to the ocean. The mountains as well as the valleys present
abundant evidence of this grand origin.

The flanks of all the interior ranges are seen to have been heavily
abraded and ground away by the ice acting in a direction parallel
with their axes. This action is most strikingly shown upon projecting
portions where the pressure has been greatest. These are shorn off
in smooth planes and bossy outswelling curves, like the outstanding
portions of canyon walls. Moreover, the extremities of the ranges
taper out like those of dividing ridges which have been ground away by
dividing and confluent glaciers. Furthermore, the horizontal sections
of separate mountains, standing isolated in the great valleys, are
lens-shaped like those of mere rocks that rise in the channels of
ordinary canyon glaciers, and which have been overflowed or pastflowed,
while in many of the smaller valleys roches moutonnees occur in great
abundance.

Again, the mineralogical and physical characters of the two ranges
bounding the sides of many of the valleys indicate that the valleys were
formed simply by the removal of the material between the ranges. And
again, the rim of the general basin, where it is elevated, as for
example on the southwestern portion, instead of being a ridge sculptured
on the sides like a mountain range, is found to be composed of many
short ranges, parallel to one another, and to the interior ranges, and
so modeled as to resemble a row of convex lenses set on edge and half
buried beneath a general surface, without manifesting any dependence
upon synclinal or anticlinal axes--a series of forms and relations that
could have resulted only from the outflow of vast basin glacier