Oak Creek Canyon is often referred to as a smaller cousin of the Grand Canyon. A
river gorge located just south of Flagstaff, Highway 89A weaves a charming
route through Oak Creek Canyon on its way to Sedona and Flagstaff. Oak
Creek Canyon area is situated in a Transition Zone between two great geologic
provinces: the Colorado Plateau and the Basin and Range.
The canyon has magical scenic scenes, dense woods shadow the road,
and the steep cliffs are colored in bands of red and yellow sandstone, pale
limestone, and black basalt. Oak Creek Canyon is a popular summer vacation area
with many day-hiking trails, such as the East Pocket Trail, a steep, wooded
climb to the canyon rim.
One of the prettiest and easiest hikes in Oak Creek is along the three-mile
(five-kilometer) West Fork Trail, which follows a stream past abandoned apple
orchards and into a narrow red rock canyon. At nearby Slide Rock State Park,
swimmers enjoy sliding over the rocks that form a natural water chute. This
canyon is approximately 19 kilometers long ranging in width from 0.8 to 2.5
miles, along with 250 to 610 meters in depth.
Oak Creek, a tributary of the Verde River, flows along the bottom of
the canyon and is one of the few perpetual streams in the high desert region
of northern Arizona. Oak Creek is mainly responsible for carving the modern Oak
Creek Canyon, through movement along the Oak Creek Fault, a 48 kilometers long
north-south normal fault line, is thought to have played a role as well. Sedona-Oak
Creek Canyon area offers some of the most unique and spectacular geologic features
in northern Arizona.
Because of the relatively sparse vegetation, most of these features
are easy to recognize and photograph. Some of these
geologic features are common on the Colorado Plateau of northern Arizona,
western Colorado, southern Utah, and northeastern New Mexico. Others occur in
many other parts of the American Southwest.
Oak Creek Canyon
slices through the Mogollon Escarpment to the House Mountain shield volcano
rising from the floor of Verde Valley. teau and the Basin and Range (Figure B.)
The Colorado Plateau, a 130,000-square-mile region of vast plains, high mesas,
buttes, deep canyons, volcanic fields, and isolated mountain clusters, is built
of thousands of feet of generally horizontal sandstone, shale, limestone strata, and basalt flows.
In north-central
Arizona, the southern margin of the Colorado Plateau is the Mogollon Rim, that
line of spectacular cliffs north of Sedona. The sedimentary and volcanic rock
layers that form this part of the Colorado Plateau are beautifully exposed in
the Mogollon Rim north of Sedona. In ascending order they are the Supai Group,
the Coconino Sandstone, the Toroweap, and Kaibab Formations, and the basalts of
the San Francisco volcanic field. Basalts of the Mormon Mountain volcanic field
cap the Mogollon Rim to the west of Sedona.
South of Sedona,
are dark-colored basalts of the House Mountain volcano and the white sedimentary
layers of the Verde Formation. For most of its geologic history, this part of
Arizona was a low-lying region where sediment was deposited and preserved to
form the layers of red and buff rocks exposed in the SedonaOak Creek Canyon
region.
The oldest of these
sedimentary rock units that are exposed throughout the region is the Supai
Group, deposited 310 to 270 million years ago (some sources say that the Supai
Formation is 270-220 million years old). During this time the Sedona-Oak Creek
Canyon region was a nearly flat, subtropical desert coastal plain bordered by
shallow seas, at the latitude of present-day Central America. Some sandstones. and
conglomerates were deposited by wet-weather streams. Other sandstones were
deltas, beaches, or desert dunes. Mudstones and limestones accumulated in
lagoons and the sea.
The sea advanced
and retreated across this coastal plain numerous times, leaving alternating
layers of terrestrial and marine sedimentary rocks. Arid conditions limited
life on land and fossils are mainly from species that lived in the sea. The
upper part of the Supai Group was deposited 275 to 270 million years ago
(Permian time) as extensive sand seas on an arid coastal plain. At times the
dune sand was reworked by the tides and spread along beaches, as occurs in
coastal portions of the Sahara and Namib Deserts today.
These massive
wind-deposited sandstones, well-cemented by calcium carbonate and silica, are
resistant to erosion and form most of the orange-red cliffs and buttes around
Sedona, such as Bell Rock, Courthouse Rock, Coffee Pot Rock, and Cathedral Rock.
The Coconino Sandstone (270 to 265 million years old, late Permian time) forms
the tall, nearly vertical cream-colored cliffs above the Supai Group.
Deposited as
massive sand dunes, similar to those found in the great sand seas of the Sahara
and Saudi Arabia, this sandstone represents an arid, inland environment far
removed from the sea. The Coconino Sandstone and the underlying upper Supai
Group contain very few fossils due to harsh desert conditions. The Toroweap
Formation (about 265 to 262 million years old, late Permian time) caps the
Coconino Sandstone and represents a return to an arid, coastal environment.
This thick
sandstone was once beach and shallow coastal sand. It contains beds of gypsum
that accumulated as high temperatures evaporated seawater from saturated desert
soils. Distinctive buff-colored cliffs above the Toroweap Formation mark the
Kaibab Formation (about 262 to 255 million years ago, late Permian time). This
rock unit consists of silty limestone and dolostone, and sandstone and
siltstone cemented by calcium carbonate.
The Kaibab
Formation was deposited in shallow seas and on an arid coastal plain.
Dark-colored rim rock capping the plateau is basalt from the San Francisco
Volcanic Field (Figure B, SF). Beginning about 6 million years ago, magma
(molten rock) from deep inside the Earth migrated upward along old fractures
and flowed onto the plateau surface as lava. Eruptions continued during the
period 3 million to 1000 years ago.
The basalt at Oak
Creek Vista is about 6 million years old. The basalt capping the cliffs to the
east and southeast of Sedona are old lava flows from the older (3 million to 15
million years ago) Mormon Mountain Volcanic Field (Figure B, MM). The contact
between these plateau-capping volcanic rocks and the underlying Kaibab
Formation marks a time gap in the geologic record of nearly 240 million years,
years not represented by the rock at this locality.
The uplift of the
Mogollon Highlands in central Arizona about 60 million years ago tilted the
entire sequence of Paleozoic and Mesozoic strata in the Sedona-Oak Creek Canyon
region to the north. At this time, rivers flowed from the higher Mogollon
Highlands across the Sedona-Oak Creek Canyon region toward the lowlands to the
north. Erosion by these rivers removed the Mesozoic strata that once existed
here and left deposits of sand and pebbles collectively called “rim gravels’
because they are found along the Mogollon Rim.
Between 35 and 15
million years ago, the crustal rocks of western North America were stretched,
thinned, and broken in blocks along steep cracks, called faults. This crustal
extension led to the collapse of the Mogollon Highlands. This collapse,
combined with thousands of feet of uplift of the Colorado Plateau, triggered a
drainage reversal in the Sedona-Oak Creek Canyon region. Streams now flowed
southward from the southern rim of the Colorado Plateau and the Oak Creek and
Verde River system slowly developed.
Today, continued
erosion is wearing back the cliffs of Pennsylvanian, Permian. and Neogene rocks
north of Sedona. This northward retreating line of cliffs, the Mogollon Rim, is
the southern edge of the Colorado Plateau in Arizona. Continued stretching of
the crust in the Sedona-Oak Creek Canyon region caused one of these blocks to
subside thousands of feet relative to other blocks, forming the deep basin now
occupied by the Verde River.
A high-standing
block was eroded to form Mingus Mountain southeast of the Verde Valley. About
10 million years ago molten rock (called magma inside the earth and lava when
it erupts onto the surface) migrated upward along faults and flowed onto the
land surface. A series of these lava flows south of present-day Sedona built
the House Mountain shield volcano. During this same time period, faulting and
lava flow dammed the Verde River. More than 275 feet (900 m) of sediment
accumulated as limestones, mudstones, sandstones, gypsum, and conglomerates in
these dry-climate lakes and form the Verde Formation that is exposed along the
modern Verde River valley.
The early Verde
River, lower Oak Creek, and some of their tributaries flowed in looping
meanders across broad floodplains, much like the Mississippi River do today.
During the last 6 million years regional uplift and reactivation of faults
caused these streams to down cut their channels into underlying sediments and,
eventually, bedrock. This downcutting preserved the sinuous flow pattern of
ancient streams in many canyons of the modern landscape.
Other canyons have
straight courses because they were cut by streams eroding the pulverized zones
of rock along faults. For example, several episodes of vertical movement along
the Oak Creek Fault produced a zone of shattered and powdered rock. Oak Creek
excavated this shatter zone as it extended its headwaters into the Mogollon
Rim, producing Oak Creek Canyon.
Later movement
along this fault triggered outpourings of lava that filled the canyon. The lava
cooled to form basalts that were offset as movement along the fault continued.
Today, weathering, rock falls and landslides, and erosion by the Verde
River-Oak Creek drainages continue to enlarge Oak Creek Canyon and wear back
the Mogollon Rim. Red rock mesas and buttes surrounding Sedona are monuments to
the power of these processes and record the diverse landscapes that once
existed in.
this part of North America.
