The Geology of
UtahMountainBiking.com has information about local
geology and botany sprinkled about our trail pages, in the (perhaps false) hope
that you're interested in learning more about the world under your bike tires.
For those who want to put the big picture together, we offer this treatise on the local
geology. - Bruce Argyle
Gooseberry Mesa lies just east of the intersection of the Colorado Plateau
with the Great Basin, and just south of the breaks of the Markagunt Plateau.
Erosion from the west, where the Great Basin has subsided, and from the south,
as the cliffs of the Virgin River Breaks move back into the Markagunt Plateau,
create this awesome, but temporary, landscape. The rock layers we're seeing here
were buried for 200 million years, emerging only in recent geologic time.
||Permian Period: The Hurricane Cliffs. During
the Permian period
(285-245 million years ago), western Utah was covered with ocean. The Ancestral Rockies
were in east-central Utah, and provided sediments that deposited in this
area. Sediments mixed with marine deposits to form limestone. These
deposits can be seen on the Hurricane Cliffs (to the east of I-15 as you
drive south, before descending to Hurricane, and seen again as you climb
up towards Gooseberry). Permian deposits include (bottom to top) the
Toroweap Formation, the Kiabab Limestone, then the Plympton Formation.
These hard marine deposits support the valley floor, forming the flat area
from which Gooseberry Mesa rises.
|Botany Break, #1. I get a lot of questions about this plant,
because its shiny round evergreen leaves and bright red bark make it stand
out. This is manzanita. You'll see this in many of the shadier areas on
This plant is seen mostly in southern Utah, but small patches of
manzanita species can be found in the north -- for example, on the Ogden
||Triassic Period: Muddy floodplains (early Triassic). By the Triassic Period (245-205 million years ago), the
Ancestral Rockies were eroded away. The southeast corner of the state was
a large flat floodplain, with the seashore moving back and forth over huge
mudflats. The Moenkopi Formation is formed
of layers of mud. The variable color is determined by the minerals in the
|The rippled areas on the slopes of Gooseberry Mesa are the
Moenkopi Formation. Harder layers create horizontal ridges -- the hardness
depends on the fineness of the clay grains that formed it, and the amount
of lime in the matrix.
At the top, we see the Chinle Formation (see
below), formed later in the Triassic.
||Middle Triassic: The rising of western Utah brings new
sources of sediment. In the middle Triassic, western Utah rose up.
The "break line" was the Wasatch and Hurricane Faults. Now
sediment was coming from the opposite direction, in bigger chunks -- sand
and pebbles instead of fine clay. As the Gooseberry area began to dry, layers of shale alternate with layers of conglomerate
and sandstone. This is the Chinle Formation. Erosion of Precambrian rock
from these western highlands produced the round quartzite rocks seen
everywhere at Gooseberry.
|This is the Shinarump conglomerate, part of the Chinle
Formation. As the softer matrix of the Shinarump
comglomerate weathers away, the harder river-rounded pebbles of
quartzite lie loose on the surface.
Forests grew along the edge of the
highlands. Periodic floods buried the trees, creating the petrified wood
found at Gooseberry. The wood-like objects in this photo are petrified
||Here and there, dark tubular areas are seen within the
sandstone and conglomerate. These are "fossilized" animal
burrows. The ones in the photo are about 8 inches across.
An animal, like today's muskrat, creates a burrow. When the burrow
fills in, the chemical and grains in the burrow are different from the
surrounding rock, creating differential erosion.
|The newly-risen highlands of western Utah were the source of
the sediment. River-rounded pebbles of pink and white Precambrian
quartzite (dating from 500 to 1000 million years ago) washed down and were
included in the conglomerate. Because these rocks are harder than the sand
matrix, they lie on the surface of the mesa, everywhere you look.
In this photo, chunks of fossilized wood sit near quartzite pebbles.
|| Late Triassic, Jurassic, and Cretaceous: Buried under
sediment layers. From the late Triassic through mid Jurassic Period (205-140
million years ago), the southern part of Utah was covered by deep
sand dunes. This formed the Wingate and the Navajo sandstone of Zion
National Park. In later Jurassic time, the area east of the Wasatch line became a river
floodplain (with rivers running east out of western Utah and meandering
towards the Gulf of Mexico).
|Botany Break, #2. This plant is ephedra, or "Brigham
Tea." The leaves are round green vertical sticks, with some
branching. These leaves contain the drug ephredrine, a potent stimulant
and vasoconstrictor (raises blood pressure, narrows blood vessels).
Because the Mormon pioneers were forbidden imported tea, they brewed
their own energy-booster and decongestant concoction. In honor of brother
Brigham, who probably did not approve, they called it Brigham Tea.
most of the Cretaceous (140-65 million years ago), the Gulf of Mexico spread through the middle of the
continent, covering eastern Utah. During this time, shales were deposited.
||Tertiary Period: The Great Basin subsides while
the western continent is uplifted. During the Tertiary (65 million years ago), the Rockies and Uinta
Mountains began to rise, and the entire western continent was uplifted. At
first, western Utah remained stable, and the area around Gooseberry was
covered by freshwater Lake Claron, creating the colored limestones of the
Virgin Rim and Bryce Canyon. Then, in middle Tertiary time, the Great Basin area began to slump and pull away
relative to eastern Utah. What had formerly been highland was now a
deep valley. The break-point was along the Hurricane Cliffs.
layers of Tertiary, Cretacious, and Jurassic rock began to erode way,
finally exposing the mid-Triassic rock that caps Gooseberry Mesa. The hard
Shinarump resisted erosion, protecting the skirts of Moenkopi shale
beneath it. Gooseberry Mesa came into being.
||Gooseberry Mesa is an example of "headward
erosion." Rather than becoming rounder and flatter, the entire cliff
moves back. The erosion eats "headward" into the cliff between
an erosion-resistant cap rock and an erosion-resistant basement rock. If
our illustration were Gooseberry, the higher cliff-line would be the
skirts of the mesa. The cap-rock is Chinarump Conglomerate. The basement
is Kaibab Limestone. The second (lower) cliff line would be the cliffs
above Hurricane, 10 miles away.
But erosion continues. The rock of the Colorado Plateau is being eroded at a rate of 500 vertical feet
every million years. Gooseberry Mesa will eventually wash down the Colorado
||If you like this sort of extra information about bike trails, you owe it to
yourself to buy a guidebook. As a start, may we recommend Greg Bromka's Mountain
Biking Utah. Go to our bookstore now.