Geology of the Verde Valley
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The Verde Valley, which
includes Sedona & Oak Creek Canyon, is located in the southwestern
United States, in north central Arizona. The Verde Valley is
a high desert region south of the Mogollon Rim, which is the southern
edge of the Colorado Plateau. The greater Sedona area is situated
in Arizona's famous red rock country tucked under the base of the
Mogollon Rim. This includes Oak Creek Canyon to the north and Jacks
Canyon to the southeast, plus several other more remote canyons to
the west.
In Precambrian times the Verde Valley area
was a submarine volcanic environment. What today is
known as Arizona was located at the northern edge of a drifting North
American continent. The oldest rocks visible in this area date
from about 1.8 billion years ago. Small microcontinents collided
with North America from the south where two crustal plates met in
a process known as continental accretion. This created a subduction
fault, meaning one plate slid under the other plate, which caused
volcanic activity and hot springs to form in the area. These hot
springs emitted small amounts of gold, silver and copper, which precipitated
out onto the sea floor. This is the source of the vast mineral
deposits that have been mined in the Verde Valley.
The history of the area is shown in a series
of sedimentary rock layers deposited over
millions of years. Five hundred million years
ago, the Verde Valley was a hot desert environment
that was the edge of a beach or shallow marine floodplain
area, much like this image below.
Continued movement of the continent caused a collision which
folded the rock layers in the area. This area subsisted or dropped slightly,
and a thin veneer of sediment accumulated. This is known as the Tapeats
Sandstone.
The Martin Formation formed about 165 million years later, when Arizona was below sea level again. The first plants and fishes appeared at this time, leaving a fossil record of sponges and brachiopods. Rock layers of the Martin Formation are composed of limestone and dolomite.
The Redwall Limestone was deposited next about 350 million years ago, which is the oldest and deepest rock layers now exposed in the Oak Creek Canyon area. At this time Arizona was near the equator and was a under a shallow, tropical coral sea, like the image shown below.
The Supai
Group was deposited at approximately the same time
the supercontinent known as Pangaea was forming. What would
eventually become The Verde Valley was located at the extreme west
edge of Pangaea. The mountains
called the Appalachians were being formed, and reptiles were evolving.
This wet coastline environment was at times covered by water, at
other times swamps or deltas.
The river system of the ancestral Rocky Mountains formed a floodplain 270 million years ago. The material deposited created The Hermit Formation; the rock layer on which the City of Sedona is built. Millions of years later, this soft formation eroded easily, and created the slopes at the base of many of Sedona's landforms.
