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GEOLOGY
The Waterpocket Fold defines Capitol Reef National Park. A nearly
100-mile long warp in the Earth's crust, the Waterpocket Fold
is a classic monocline: a regional fold with one very steep side
in an area of otherwise nearly horizontal layers. A monocline
is a "step-up" in the rock layers. The rock layers on the west
side of the Waterpocket Fold have been lifted more than 7000 feet
higher than the layers on the east. Major folds are almost always
associated with underlying faults. The Waterpocket Fold formed
between 50 and 70 million years ago when a major mountain building
event in western North America, the Laramide Orogeny, reactivated
an ancient buried fault. When the fault moved, the overlying rock
layers were draped above the fault and formed a monocline.
More recent uplift of the entire Colorado Plateau and the resulting
erosion has exposed this fold at the surface only within the
last 15 to 20 million years. The name Waterpocket Fold reflects
this ongoing erosion of the rock layers. "Waterpockets" are
basins that form in many of the sandstone layers as they are
eroded by water. These basins are common throughout the fold,
thus giving it the name "Waterpocket Fold". Erosion of the tilted
rock layers continues today forming colorful cliffs, massive
domes, soaring spires, stark monoliths, twisting canyons, and
graceful arches.
Capitol Reef
The most scenic portion of the Waterpocket Fold, found near the
Fremont River, is known as Capitol Reef: "capitol" for the white
domes of Navajo Sandstone that resemble capitol building rotundas,
and "reef" for the rocky cliffs which are a barrier to travel,
like a coral reef.
Nearly 10,000 feet of sedimentary strata are found in the
Capitol Reef area. These rocks range in age from Permian (as
old as 270 million years old) to Cretaceous (as young as 80
million years old.) The Waterpocket Fold has tilted this geologic
layercake down to the east. The older rocks are found in the
western part of the park, and the younger rocks are found near
the east boundary.
This layer upon layer sequence of sedimentary rock records
nearly 200 million years of geologic history. Rock layers in
Capitol Reef reveal ancient climates as varied as rivers and
swamps (Chinle Formation), Sahara-like deserts (Navajo Sandstone),
and shallow ocean (Mancos Shale).
 Cathedral
Valley
The tilt of the Waterpocket Fold dies out at Thousand Lake
Mountain near the northwestern boundary of the park. Rock layers
in Cathedral Valley have a gentle inclination of 3 - 5 degrees
to the east and appear nearly horizontal.
Deep erosion has carved Cathedral Valley's free-standing monoliths,
or temples, out of the soft reddish-orange Entrada Sandstone,
which was originally deposited as sandy mud on a tidal flat.
Some of the cathedrals are capped by thin, hard beds of a greenish
gray marine sandstone, the Curtis Formation.
The scenery of the Entrada Sandstone temples of Cathedral
Valley is complemented by evidence of other geologic processes
at work. Flowage and dissolution of gypsum, a soluable mineral
from the underlying Carmel Formation, created Glass Mountain
and the Gypsum Sinkhole. Glass Mountain is an exposed plug of
gypsum. The Gypsum Sinkhole formed when a gypsum plug dissolved.
Dikes and sills, which are thin bodies of igneous rock and small
volcanic plugs, are found in Upper Cathedral Valley. These features
formed during volcanic activity 3 to 6 million years ago.
Erosion
Most of the erosion that carved today's landscape occured after
the uplift of the Colorado Plateau sometime within the last 20
million years. Most of the major canyon cutting probably occured
between 1 and 6 million years ago.
Even in this desert climate, water is the erosional agent
most responsible for the carving of the landscape. The pull
of gravity, in the form of rock falls or rock creep, plays a
major role in the shaping of the cliff lines. Wind is a minor
agent of erosion here.
The landforms are a result of different responses of the various
rock layers to the forces of erosion. Hard sandstone layers,
like the red Wingate and the white Navajo Sandstones, form cliffs.
Softer, shale layers, like the Chinle Formation, form slopes
and low hills. The barren slopes found in many areas are due
in part to the presence of bentonitic clays in the shale which
make an inhospitible environment for plants.
The black boulders, found scattered throughout the Fremont
River valley and along other drainages, are recent geologic
arrivals to Capitol Reef. These volcanic rocks came from the
20 to 30 million year old lava flows which cap Boulder and Thousand
Lake Mountains. The boulders made their way to Capitol Reef
during the Ice Ages when the High Plateaus supported small mountain
glaciers. Landslides, debris flows, and possibly heavy stream
outwash from these glaciers carried the boulders to lower elevations
in the park.
Capitol Reef National Park was established because of the scenic
rock domes and narrow canyons found along the trace of the Waterpocket
Fold. Indeed, the park boundaries were drawn to encompass most
of the Fold. Capitol Reef is a place to enjoy the scenic majesty
formed by geologic processes, and also to appreciate the interrelationships
between the Earth and all life found in the varied environments
within the park - - from the forested slopes of Thousand Lake
Mountain, to the green oasis of Fruita, to the barren Bentonite
Hills. |
