The foreground in
this view to the west illustrates how Unkar Creek’s debris fan
deflects the Colorado River. Unkar Creek originates off the
North Rim (right) and drains the easily eroded Dox Formation.
The large amount of debris that it deposits pushes the river
to the left out of its normal course.
In relatively recent times, some of these debris
flows have created small dams at Unkar Delta. The river would
then back up and deposit a lot river gravel upstream from
these dams before it could cut back down to its original
level. Remnants of these old river gravel deposits are still
visible along both sides of the river for half a dozen miles
A few miles further downstream the up-to-the-west
tilt of the Grand Canyon Supergroup brings the much harder
Shinumo Quartzite above ground level to form a cliff just
before the river turns westward.
The small segment of the South Rim visible in the
upper left corner is Shoshone Point (a few miles east of Grand
Canyon Village), while Wotans Throne, Cape Royal, and a small
section of the Walhalla Plateau (North Rim) can be seen in the
upper right corner.
The river gradient continues steeper in the
western Dox area than it was east of the Butte Fault. Then,
the steepest river gradient in the entire Grand Canyon is
encountered in the area around Hance Rapid after the sharp
bend in the river toward the west-northwest.
View to the
west-northwest. In the foreground the Colorado River turns
a corner and plunges down Hance Rapid with the average
river gradient in this section (about 18 ft/mi) the
steepest in the Grand Canyon. The steep gradient is a
result of three different factors. First, the debris fan
from Red Canyon (enters from left edge) would normally
create a rapid. Next, this area is on the west (downhill)
side of the axis of the Kaibab Plateau. Finally, the river
is crossing from the hard Shinumo Quartzite to the more
easily eroded underlying Hakatai Shale.
As part of the Grand Canyon Supergroup, the
Hakatai Shale also tilts upward to the west and forms a
small upward tilting slope in the right side of the canyon
just below Hance Rapid. Then at the river's leftmost
position in the picture, the Bass Limestone and Vishnu
Schist are encountered and the river enters Upper Granite
River mile 80 is reached where the river
turns slightly further to the right before disappearing
from view. Cottonwood Creek enters from the left just
after this bend to the right.
miles 64 to 72
river miles 80 to 88
the Index Page for the Grand Canyon Tour
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