For eight or ten miles below the mouth of the Little Colorado, the river
is in the variegated quartzites, and a wonderful fretwork of forms and
colors, peculiar to this rock, stretches back for miles to a labyrinth
of the red-wall cliff; then below, the black gneiss is entered and soon
has reached an altitude of 800 feet and sometimes more than 1,000 feet,
and upon this black gneiss all the other structures in their wonderful
colors are lifted. These continue for about seventy miles, when the
black gneiss below is lost, for the walls are dropped down by the West
Kaibab Fault and the river flows in the quartzites.
Then for eighty miles the mottled (or alcove) sandstones are found in
the river bed. The course of the canyon is a little south of west and is
comparatively straight. At the top of the red-wall limestone there is a
broad terrace, two or three miles in width, composed of hills of
wonderful forms carved in the banded beds, and back of this is seen a
cliff in the tower limestone. Along the lower course of this stretch the
whole character of the canyon is changed by another set of complicating
conditions. We have now reached a region of volcanic activity. After the
canyons were cut nearly to their present depth, lavas poured out and
volcanoes were built on the walls of the canyon, but not in the canyon
itself, though at places rivers of molten rock rolled down the walls
into the Colorado.
The canyon for the next eighty miles is a compound of that found where
the river is in the black gneiss and that found where the dead volcanoes
stand on the brink of the wall. In the first stretch, where the gneiss
is at the foundation, we have a great bend to the south, and in the last
stretch, where the gneiss is below and the dead volcanoes above, another
great southern detour is found. These two great beds are separated by
eighty miles of comparatively straight river.
Let us call this first great bend the Kaibab reach of the canyon, and
the straight part the Kanab reach, for the Kanab Creek heads far off in
the plateau to the north and joins the Colorado at the beginning of the
middle stretch. The third great southern bend is the Shiwits stretch.
Thus there are three distinct portions of the Grand Canyon: The Kaibab
section, characterized more by its buttes and salients; the Kanab
section, characterized by its comparatively straight walls with
volcanoes on the brink, and the Shiwits section, which is broken into
great terraces with gneiss at the bottom and volcanoes at the top.