View to the
northwest with Blacktail Canyon slightly below the center
while Forster Canyon enters from the left edge. The South Rim
stretches across the top edge with Fossil Canyon near the
center, and reaches out toward Great Thumb Point at the upper
The Tapeats Sandstone and Bright Angel Shale
layers are once again next to the river, as the Precambrian
layers have not been exposed here yet. The Colorado River
straightens out for a few miles and serenely marches down
Conquistador Aisle - bordered on both sides by massive cliffs
of Redwall/Muav Limestone.
The Kaibab/Toroweap/Coconino complex still forms
the cliff at the rim, but the broad flat Esplanade Sandstone
surface is becoming more prevalent. The Esplanade surface
defines what was here before the Colorado River overflowed the
Kaibab Plateau about 5.4 million years ago. Earlier in the
Miocene, the Hualapai drainage system had eroded broad canyons
down to the Esplanade surface. By 6 million years ago this
area looked like many other areas in the southwestern U.S.
that are characterized by broad valleys that are bounded by
steep canyon walls rising abruptly up to flat-topped mesas.
When the river started flowing through here about 5.4 million
years ago, it quickly eroded downward to cut the inner canyon.
View to the
northeast with Fossil Canyon and Great Thumb Point on the
left (South Rim) side of the river. A piece of the Powell
Plateau (North Rim) can be seen in the upper right corner.
128 Mile Canyon is not exactly noteworthy, but it joins
the right hand side of the river just after it bends back
slightly to the right.
Fossil Canyon is aptly named. The Bright
Angel Shale in this area has many fossils over 500 million
This part of the river (that section that
flows northeastward) is also interesting as it is flowing
into rising strata layers. (Also rising surface topography
if you disallow the canyon.) At one time it was thought
that a "pirate stream" eroding from the west side of the
Kaibab Plateau captured an ancestral Colorado River that
existed to the east of the plateau. However, this would
require the headwall erosion of the "pirate stream" to
actually work its way back downhill through this section.
This is of course impossible which is one of the reasons
we can confidently say there was no "pirate stream".
Return to river miles 112 to 120
river miles 128 to 136
the Index Page for the Grand Canyon Tour
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