View to the west
with contour intervals at 100 feet. Highway I-70 uses this
breach across Utah's Wasatch Plateau. Surface layers are
mostly the Mesa Verde Group, and many faults cut north to
south (right to left) across the area as part of the
Sevier/Wasatch Fault system.
Salina Creek flows
east to west (foreground to background) through this breach
point now, but it is just a local stream opportunistically
using a route pioneered by the Colorado River. As shown by the
flattish areas in the foreground and middle background, Salina
Creek currently has little cutting power.
The Colorado River developed a westward route
through this area when uplifts near the end of the Oligocene
in Colorado's Rabbit Ears Range and across southern Wyoming
blocked earlier drainage northward into Wyoming. The river
stayed here until about 5.4 million years ago.
During the Miocene, basin and range stretching
was opening evaporative basins in western Utah. Since the
climate was even drier than it is now, the ancestral Colorado
evaporated leaving a lot of silt and salt as sediments. The
source of the salt was what the upstream portions of the river
leached out of Paradox Basin (in southeast Utah/southwest
Colorado). Today, the Humboldt River in northern Nevada is a
model for what the Colorado River was like in early to mid
The Wasatch Ranges started rising during the
Miocene and by 10 million years ago started to obstruct the
Colorado's old route into western Utah. As the ranges rose,
the river had an increasingly difficult time maintaining its
old path, and a massive backup system formed east of here.
Silt deposits backed up into northwest Colorado (the Browns
Park Formation) and extended southward across the Hopi Lake /
Bidahochi area in eastern Arizona. About 5.4 million years
ago, the backup system overflowed the Kaibab Plateau at the
present location of the Grand Canyon. The Colorado River
abandoned this route across the Wasatch and started digging
the Grand Canyon. However, local drainage within the rising
Wasatch could still feed into this old breach point.
20,000 years ago, large areas of western Utah
were part of freshwater Lake Bonneville, but subsequently the
climate has become drier, and the lake has shrunk to the
current Great Salt Lake. Salt in the lake as well as the
surface salt layers in Utahís western deserts has leached out
of the sediments that were left behind in the basins.
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