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