Junction of the Little Colorado River and the Colorado
Grand Falls of the Little Colorado River
The relief/topo map at
the right shows the junction of the Little Colorado River and
the Colorado River just to the east of the main portion of
Grand Canyon National Park. The Colorado River enters from the
upper left corner and flows south and southwestward to exit
off the left edge. The Little Colorado River enters from the
lower right edge and flows generally north and northwestward
to join the Colorado River in the upper left quadrant. Note
that the two rivers flow in opposite directions for a
considerable distance - a point that we will come back to.
Short sections of U. S. highway # 89 (red road)
can be seen in the right corners while Arizona highway # 64
(the east entrance to Grand Canyon National Park) can be seen
across the lower half of the map. Cameron, Arizona is in the
lower right corner.
The Little Colorado River is of interest as it
has played a part in both the oldest and most recent
derivation of the Colorado River drainage system. Before the
Rocky Mountains first began to rise some 70 million years ago,
river drainage was from southwest to northeast across this
area. As the Rockies rose they blocked the southwest to
northeast drainage, and the ancestral Little Colorado drainage
was established. Since this drainage could not go through the
rising Rockies, the Little Colorado established an “end run”
around the Rockies.
Here in Arizona, the initial drainage was from
southeast to northwest (essentially what we see now and
continuing northwestward across what would become the Kaibab
Plateau), then north through south-central and eastern Utah,
and finally northeastward through northwestern Colorado and on
into present day Wyoming. The first uplift of the Kaibab began
shortly after this ancestral river route was established. Part
of this initial route of the Little Colorado would be reused
by the Colorado in subsequent events when the Colorado would
eventually relocate to Arizona tens of millions of years
40 million years ago, there was a second uplift
of the Kaibab Plateau which forced the Little Colorado to
relocate further to the east, but the ancestral path of the
Little Colorado would leave a relatively low route across the
If we keep following the clock forward, by 15
million years ago, the lower right portion of the map area
(and for a considerable distance off the lower right edge) had
subsided into a closed basin with little if any outward
drainage. It was basically a “playa” that would hold a shallow
lake during wet periods, but would be dry much of the time. At
one time it was theorized that a large lake (Hopi Lake)
occupied the area, but recent evidence shows that no large
lake ever existed here. (If nothing else, the climate is too
In the last few million years, as the climate has
cooled and precipitation has increased, the Little Colorado
River has once again become a contributor to the Colorado
River system. The current path of the Little Colorado gives us
some clues as to what happened to local topography and when it
The Hopi Butte Volcanic field (well off the lower
right edge of the map) was active 5.5 million years ago when
the Colorado River abandoned its route across Utah (in
response to uplift of the Wasatch Plateau) and established a
new route over the ancestral low route across the Kaibab. In
the Hopi Butte volcanic field, there are dikes and sills below
about 6,300 feet elevation but surface lava flows and volcanic
ash above 6,300 feet. This tells us that 5.5 million years ago
the ground surface not to far from the map area was near 6,300
feet above sea level.
Current elevations in the map area range from:
1) Over 7,000 feet on the Kaibab Plateau in the lower left
2) Down to 6,000 to 7,000 feet in between the Little Colorado
and Colorado Rivers;
3) Down to below 4,200 feet in the lower right corner;
4) Down to about 2,700 feet in the bottom of the Grand Canyon.
When the Colorado River established its current
course, the most recent uplift of the Kaibab Plateau hadn’t
begun yet as the path of the Colorado doesn’t show any
deflection to avoid the Kaibab. Thus 5.5 million years ago
there was a nearly level surface at about 6,300 feet (level
with the Hopi Butte Volcanic Field) that led into the
ancestral low area across the Kaibab.
The Little Colorado River is deflected by the
Kaibab as it turns north before turning west to join the
Colorado. It also flows parallel to the topographic contours.
The slope is down to the right and up to the left. We thus get
the following sequence of events:
1) 5.5 million years ago the Colorado River relocated to
Arizona. It was not deflected by the Kaibab, and side erosion
began to develop side canyons into the Colorado.
2) The Kaibab Plateau began its most recent uplift. The
Colorado River became entrenched and started to cut the Grand
3) On the order of one to two million years after the Colorado
River became established, rainfall in the local area increased
to the point that the Little Colorado River could overflow its
basin. However, the Kaibab had risen somewhat with the result
that the Little Colorado was deflected further north around
the east side of the Kaibab until it could connect with a side
canyon leading into the main Colorado.
4) As the Kaibab continued to rise (about 1,400 feet
over the last 5.5 million years) both rivers have cut deep
canyons into the rising terrain. The very steep sides to the
Little Colorado Gorge attest to very young erosion.
of the Little Colorado River
The relief map above is centered some 30 to 35
miles to the south-southeast of Cameron, Arizona. The Little
Colorado River enters from the lower right edge and flows
northwestward to exit off the upper left corner. Actually, the
river “flows” only during wet periods and can be just a dry
sandy bed for long periods.
Before it gets close to the Colorado River, most
of the Little Colorado’s path across Arizona crosses very flat
land. However the relief map shows a couple of areas of
interest. Contour lines at 50 foot intervals show a small
canyon complex in the lower right portion of the map, and a
deeper canyon in the upper left.
This area is just to the east of the Sunset
Crater/San Francisco Peaks volcanic field. Sunset Crater
erupted just a thousand years ago, and there are many dozens
of other nearby cinder cones and basaltic lava flows of recent
origin. The volcanic field sits on top of a hot spot where
magma is rising from deep under the earth’s crust.
Magma from the volcanic field manifests itself in
1) The magma can intrude between in rock layers below the
surface. An intrusion acts like a blood blister and lifts the
rock layers above it.
2) The magma can rise to the surface to produce a volcanic
eruption. This can include lava flows as well as cinder cones.
The canyons that can be seen in the relief map
are the result of uplifts over intrusions. When surface rock
is uplifted, it becomes an obstacle to any river system than
runs through the uplift. River and stream systems carry mud
and sand, and these particles can abrade anything that “gets
in their way”. The canyons that can be seen in the map are the
result of thousands of years of abrasion by the Little
Colorado River and some of its tributaries.
The upper left canyon shows the next step in the
process. Initially, the Little Colorado River abraded a canyon
several hundred feet deep by the above process. The next thing
that happened was a surface lava flow.
The Google Earth picture above shows what
happened after a lava flow entered from the left side of the
picture. (About 20,000 years ago http://bulletin.geoscienceworld.org/cgi/content/abstract/118/3-4/421
The lava flow filled in part of the canyon and then continued
some three-quarters of a mile to the northeast of the old
canyon. Mud and silt have filled in the old upstream side of
the canyon (foreground in the picture) while the river has
been diverted around the lava flow. The river bed returns to
the older canyon on the far side of the lava flow. When the
Little Colorado River does flow, it forms a waterfall where it
pours over the edge of the older canyon.
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