View to the north
showing Gore Canyon where the Colorado River cuts east to west
through the Gore Range. Contour lines at 100-foot
intervals. Kremmling, Colorado is to the right (east) of
the canyon. Also, an abandoned high valley cuts east to west
through the range just south of the canyon. The valley was
originally cut by the Blue River (which currently flows
northward from the lower right edge), but the Blue gave up on
this route and now continues north to join the Colorado just
to the east of the canyon.
In theory the Colorado River could take an easier
route following the valley to the north - staying east of the
Gore Range. Ultimately it would go over Muddy Pass which is
currently 600 feet lower than the rims of Gore Canyon. How and
why did the river take this seemingly more difficult route
through the Gore Range?
There appear to be two separate Gore Ranges as we
go back in time. The first range rose during the Laramide
mountain building period some 65 to 70 million years ago. The
ancestor of the Colorado River stayed east of the original
Gore Range and flowed northward from Kremmling into Wyoming.
During the Paleocene and Eocene this original Gore Range
eroded down to a nearly flat surface. Then the Rabbit Ears
Range (northeast of here) rose during the Oligocene blocking
the old northward drainage.
The river turned west-southwest to its present
course. The Blue River also turned west and joined the
Colorado at the west end of the present canyon. Then, the
major uplift of the current Gore Range started during the
Miocene. It is probable the Gore Range is still rising today.
As the Gore Range rose, both rivers tried to maintain their
established routes by cutting downward. Bedrock in the Gore
Range is very hard Precambrian gneiss and schist. The Blue
River didn't have the cutting power of the Colorado and its
down cutting gradually lagged behind that of the Colorado. The
northwest to southeast valley to the right (east) of the range
has much softer Tertiary and late Cretaceous deposits that
erode easily under ordinary weathering. Eventually the Blue
River abandoned the old high valley and relocated to its
present location to join the Colorado east of the canyon.
Also, please see http://www.durangobill.com/PaleoAppendPart7.html
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