View to the west
from Dotsero to Glenwood Springs, Colorado. Contour intervals
are 100 feet. The major highway is I-70. The Colorado River
cuts through the south side of the White River Plateau to form
Glenwood Canyon. Cottonwood Pass Road (Near electric
transmission lines to the left) crosses Cottonwood Divide some
1,000 feet lower than the average height of the canyon's rims.
Glenwood Canyon is an interesting study in how
rivers get into canyons. Cottonwood Divide (lower route to the
left around the plateau) is capped with Tertiary lava. Hence
it has never been much higher than it is now. The rims of
Glenwood Canyon are capped by Mississippi and Pennsylvanian
Limestone and would be higher yet if you travel back in time
to restore layers that have been eroded away. Even more
interesting, upstream from here, the Colorado River could
escape to the north near Yampa, Colorado and still stay 1,000
feet lower than the current rims of Glenwood Canyon. Why did
the river establish a path across the higher surface?
We go back to our rule that rivers will always
take the easiest available path when they first become
established. When the Colorado River turned westward by early
Miocene time, the White River Plateau had not risen yet. Then
after the river had established its course, the plateau rose
during the rest of the Miocene. (Recent research indicates
much of this uplift has occurred in the last 5 million years.)
By the time the plateau started to rise, the river was stuck
in a rut. As the plateau rose, the "rut" just got deeper.
It is probable the plateau is still slowly rising
with the river cutting ever deeper. The sheer sides of the
canyon and steep gradient of the river through it are classic
signs of recent activity.
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