View to the
northwest with Elves Chasm in the lower left quadrant where
the river turns to the right and continues behind Explorers
Monument. Then, Blacktail Canyon enters from the right near
the center of the picture where the river bends back to the
left. Apache Point on the South Rim is in the upper left
quadrant. Some of the oldest rock in the Grand Canyon is found
near river level at Elves Chasm. It has been dated at 1.84
billion years old.
The Monument Fold (Fault) enters the picture
slightly to the left of the center of the bottom edge, then
passes slightly to the right of Explorers Monument, and then
curves a little to the left to cross the river again. Strata
to the right (northeast) of the Monument Fold are displaced
downward. Thus the Precambrian layers drop below river level
downstream from the Fold, and the slope associated with the
Bright Angel Shale is brought down to river level near
Blacktail Canyon. If you have a Belknap's River Guide, please
note that the up/down thrown sides of this fault are labeled
incorrectly. As can be seen in this picture (and as labeled on
the Geologic Map of the Grand Canyon) it is the left
(southwest) side of this fault that is uplifted.
Blacktail Canyon is one of the best places to see
the 1-billion year age gap that forms the boundary between the
Tapeats Sandstone and the underlying basement rock.
Unfortunately, the resolution of the picture is not great
enough to illustrate this, but if you are rafting the Colorado
River, this boundary is clearly visible a short distance up
miles 104 to 112
to river miles 120 to 128
the Index Page for the Grand Canyon Tour
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