lava
Eocene Wasatch: Pink Cliffs ROCKS IN BRYCE CANYON PARK
MESOZOIC
Cretaceous Undifferentiated: Gray Cliffs
sandstone
shale
coal
Jurassic
gypsum
Carmel limestone
Navajo sandstone: cross-bedded ROCKS IN ZION PARK
White Cliffs sandstone
Kayenta-Wingate
Triassic
Chinle: Vermilion shale,
Cliffs sandstone,
ash and
limestone
fossil wood
Shinarump conglomerate
Moenkopi: Belted shale
Cliffs
sandstone
oil RIM OF GRAND CANYON
Permian Kaibab limestone
A study of the rocks of Zion and Bryce Canyon shows that during the last
200,000,000 years the region comprising the parks has witnessed many
changes in landscape and climate. At times it was covered by the sea, at
other times broad rivers traversed its surface, and at still other times
it was swept by desert winds. Most of the rocks were laid down by water
as gravel, sand, mud, and limy ooze. They have been converted into solid
rock by the weight of layers above them and by lime, silica, and the
iron that cement their grains. Embedded in the rocks are fossil sea
shells, fish, trees, snails, and the bones and tracks of land animals
that sought their food on flood plains, in forests, or among sand dunes.
The most conspicuous remains are those of dinosaurs--huge reptiles that
so dominated the life of their time that the Mesozoic is known as the
"age of dinosaurs."
The accumulation of some 8,000 feet of strata (Mesozoic and Tertiary) on
top of 4,000 feet of older (Paleozoic) beds, which are exposed in Grand
Canyon, may be considered the first of three major events in the
development of the marvelous landscapes of the Zion-Bryce region; it
provided the material from which the huge scenic features were later
carved. The second event was a regional uplift which elevated the
previously low-lying top beds of the series (Wasatch, Pink Cliffs) to a
height of nearly 2 miles above sea level. As a result of this movement,
the earth's crust was broken into huge rectangular blocks by north-south
fractures or faults. Three of these great faults can be seen in the
vicinity of the parks: the Hurricane fault in the Hurricane Cliffs, west
of Zion; the Paunsaugunt fault in the cliffs of Bryce; and the Sevier
fault along the Mount Carmel Road between the two parks.
In consequence of the uplift the third major event, the present cycle of
erosion, was initiated. The streams became strong and swift and so were
able to cut deeply into the underlying rock and carry away the land
waste. In this process the streams have removed many cubic miles of
rocks, which, if replaced, would fill the present canyons and build up
their bordering land to the level of the lofty Markagunt and Paunsaugunt
Plateaus. The gigantic features of Zion and Bryce Canyon National Parks
mark a stage in the process of erosion that began long ago and which, if
continued without interruption, will convert the present rugged
landscape into plains near sea level.
_Distinctive Features of Bryce Canyon._--In its regional setting Bryce
Canyon National Park is the southeastern border of the extensive
Paunsaugunt Plateau. It comprises two areas of strongly contrasted
topography that meet in a line that marks the rim of the plateau and the
top of its bordering cliffs. Back from the rim the plateau surface on
which the park buildings and the automobile roads have been constructed
is generally flat land traversed by broad, shallow valleys in which
erosion is inconspicuous. Below the rim erosion has produced a region of
remarkable ruggedness. It might naturally be supposed that the beautiful
amphitheater at the head of Bryce Canyon had been carved by waters
pouring down from the plateau above. But the plateau streams contribute
nothing; they flow away from the rim. The chief sculpturing agents are
the rain and snow that fall directly into the canyon. In producing the
amazing variety of erosion features the streams have been aided by frost
that pries fragments from the cliffs and by chemical agencies that
decompose the rock and supply its vivid color.
The development of the park landscape was made possible by movements
within the earth's crust which brought originally low-lying strata to an
altitude exceeding 8,000 feet. Streamways on the flat top of this
uplifted block were little affected, but with greatly steepened
gradients the streams around the borders of the newly made plateau
became powerful. The Paria and its swiftly flowing tributaries have cut
deeply into the face of the Paunsaugunt and carried billions of tons of
ground-up rock to the Colorado. At the present time erosion by Bryce
Creek, Yellow Creek, Willis Creek, Podunk Creek, and many smaller
streams, is causing the plateau face to retreat northwestward, and these
streams are taking into their drainage areas channels that formerly
carried waters northward to Sevier River.
The drab-colored landscape along the southeast border of the park has
been developed in alternating beds of shale, coal, and sandstone
(Cretaceous age); in the resulting erosion forms, slopes, mounds,
rounded ridges, and valleys with inclined or steplike sides predominate.
The brightly colored rocks that form the topmost cliffs and terminate
abruptly in such headlands as Steamboat Mountain, Bryce Point, and
Rainbow Point are resistant limestones of Tertiary age (Wasatch
formation). They erode as vertical walls (Pink Cliffs), which weathering
has developed into the astonishing display of architectural forms that
make Bryce Canyon distinctive.