August 2024
(Zion, Bryce, Canyonlands, Arches National Parks)
Click on all photo's for larger
images
Zion Canyon from Observation
Point
(A Storm system can be seen in
the background which we got caught in on the way back)
A little (very little) Geology of
the Colorado Plateau and the Grand Staircase
Colorado Plateau
The Colorado Plateau is one of roughly
two dozen geographical provinces of the United States. It covers
130,000 square miles of the four corners region of the southwestern
United States (clockwise; Utah, Colorado, New Mexico, Arizona).
Beginning around 80 million years ago geological forces began
to uplift the plateau, first slowly (geologically speaking), then
around 25 million years ago the uplift accelerated to about 130
feet/million years, then 730 feet/million years around 5 million
years ago and it continues to rise today. The cause of the uplift
is thought to be the collision of the North American Plate and
the Farallon Plate, causing the Farallon plate to subduct and
generate heat that drove the Colorado Plateau upward to its current
elevation. The plateau is currently situated about 1 mile above
sea level. The plateau remarkably records hundreds of millions
of years of geologic time within its almost 200 sedimenatary rock
formations. The formations consist of mostly sandstones, shales
and limestones, deposited as the region experienced a wide variety
of climates (dessert, tropical, lakes and river beds, Marine).
The rock formations are revealed today in outcroppings and canyons
as the red, white, gray, green, and yellow sedimentary rock formations
revealed and sculpted by the erosive forces of rivers, rain, frost,
and wind. The Colorado Plateau is now home to ten National Parks,
27 National Monuments, 19 National forests, and 57 State Parks.
In one of the most remarkable geologic
landscapes on earth nearly two billion years of rock layers are
exposed over 100 miles of the Colorado Plateau in a stepwise fashion
(East to West) from the highest and youngest formation at Bryce
National Park to the deepest and oldest formation at the bottom
of the Grand Canyon. The youngest rocks, just 45 million years
old, make up the Pink Cliffs in Bryce Canyon. Progressing backward
in time are the Gray Cliffs of Sandstone and Shale, the Whitish-red
Cliffs of Zion National Park (Navajo Sandstone), the reddish Vermillion
Cliffs, and the Chocolate Cliffs (mudstone). As we progress southwest
this portion of the Grand Staircase experienced its own separate
uplift, known as the Kaibab uplift, which set the stage for the
formation of the Grand Canyon. Around 5 million years ago the
Colorado River formed and its erosive forces have since carved
the Grand Canyon, slicing through 500 million years of sedimentary
rock layers finally arriving at the 1.8 billion year old Vishnu
Schist, the oldest exposed rock on the Colorado Plateau.
Zion National Park
We began our tour of Southern Utah National Parks at Zion National
Park. Canyons are typically formed by the erosive forces of rivers.
The Grand Canyon was formed by the Colorado River over a period
of about 5 million years. Similarly Zion Canyon was formed by
the erosive forces of the Virgin River. The Virgin River originates
at Navajo lake, 9000 feet above sea level, flows south for about
160 miles across the Utah border into Arizona and Nevada, ultimately
emptying into Lake Mead. Although the Virgin River flow rate is
only 1% of the mighty Colorado River, the Virgin has a much steeper
gradient falling 7800 feet during its course, nearly 10X steeper
than the Colorado River. During floods (of which there are plenty)
the Virgin River can erode a massive amount of sediment, rocks,
and boulders which is how it carved Zion Canyon in only two million
years. The Virgin River floods have sliced through 2000 feet of
Navajo sandstone creating the massive cliffs which line the canyon
in Zion.
Navajo sandstone is everywhere you look in Zion. Where did it
come from? Beginning around 190 million years ago (in the early
Jurassic) Utah was home to the largest desert that ever existed
on earth covering around 150,000 square miles. Over a period of
30 to 40 million years the sand gathered to a depth of over 2200
feet forming what would later be the Navajo Sandstone formation.
At around 160 million years ago sea levels rose and an inland
sea covered the sandstone. Where did all that sand come from?
Turns out that around the same time period the ancient Appalachian
mountains where attaining heights comparable to today's Himalayan
mountains. Tall mountains erode quickly and their erosion debris
was carried south by wind and an ancient massive river system
to ultimately form the greatest desert ever.
Zion Canyon from Observation
Point
"The Narrows" Hiking
in the Virgin River
Hiking in the Virgin River
(The Narrrows)
Click HERE
for a video of hikers ascending to Angels Landing
Bryce Canyon National Park
Our next stop was Bryce Canyon only
an hour 40 minutes from Zion. Bryce is well known for a very specific
rock formation known as a Hoodoo. Bryce sports the largest and
densest collection of Hoodoo's in the world. Hoodoos are pillars
of mostly sandstone created by the processes of uneven weathering
(chemical and physical processes that break up rocks) and erosion
(removal of sediment and rock due to weathering). The uplift of
the Colorado Plateau caused the area that is now Bryce Canyon
to move to a higher elevation, in some areas 10,000 feet above
sea level. Because of its high elevation the region experiences
freezing temperatures at night for around 200 days of the year.
When plateaus of rock are uplifted there are natural vertical
faults and cracks which occur. Water seeps into these spaces between
the rocks. When the temperature lowers, the water within the rock
freezes and expands which in a process called ice wedging. This
expansion begins to break apart the rocks, first into walls (known
as fins), then windows (or arches), then a fully formed hoodoo
as water continues to melt and then refreeze and reenter the cracks.
Hoodoos are distinguished from rock spires or towers by their
resemblance to totem poles, in that they have very selective erosion
causing parts of the hoodoo (usually the top) to be wider than
other parts.
The Hoodoos are usually capped by a type of rock which is more
resistant to erosion (such as compressed sandstone, limestone,
or dolostone) which protects the layers immediately below it.
As softer sandstone below erodes away the protected sandstone
above it retains its shape…..hence a Hoodoo.
The "Wallstreet"
section of the Bryce Amphitheater
Bryce Amphitheater
Hoodoos along the Queens
and Navajo Trail
Navajo Trail
The "Wallstreet"
section of the Bryce Amphitheater
A lone Hoodoo showing the
typical pattern of selective erosion of sandstone with preservation
of the "cap" made up of more erosion resistant limestone.
Arches National Park has the densest
concentration of natural arches in the world. There are over 2,000
arches in the park, ranging from sliver-thin cracks to spans greater
than 300 feet. How does an arch form? The area of Arches National
Park was uplifted beginning around 65 million years ago by a combination
of factors including the Colorado Plateau uplift and expanding
underground salt layers (from ancient oceans). Because of its
particular type of sedimentary rock (Entrada sandstone) the uplift
first caused immense parallel cracks in the uplifted rock. Thus
began the erosive process. Rain seeped into the long parallel
cracks creating huge wall-like rock formations with smooth round
edges known as "fins". The Entrada sandstone which forms
the arch is very permeable to water and delivers it to the layers
of rock below which is more easily eroded. The erosion preferentially
affected the inner material of the fin and along with gravity,
and physics, a hole was formed ultimately creating a natural arch.
James alongside the 54 foot tall
Delicate Arch
Delicate Arch and the "bowl"
Balanced Rock
A grouping of "Fins"
the precursor of natural arches. The fins will begin to erode
from bottom up forming a hole which will further erode forming
an Arch.
A "Fin" from another
perspective
Canyonlands
Canyonlands National Park was our
last stop. Canyonlands is vast and desolate but also imposing
and beautiful. Similar to the Grand Canyon and Zion Canyon, Canyonlands
was formed by river systems; the Green River and Colorado Rivers.
Canyonlands National Park contains a wide variety of sedimentary
rock types including sandstone, siltstone, mudstone, limestone,
and bedded gypsum. Sandstone however is the most prevalent rock
type in the park. The sedimentary rocks of Canyonlands were deposited
between about 310 and 160 million years ago. The layers lay unexposed
until the Green River and Colorado River systems cut into the
landscape, within the last 3 million years, exposing the sandstone
cliffs. Rain continued the process eroding the cliffs back and
widening the Canyon.
Canyonlands Landscape
Canyonlands Sandstone cliffs
Moab Giants Dinosaur Museum
Lifesize Trex model at Moab
Giants Dinosaur Museum
Theropod Dinosaur tracks
found in Moab. Moab is known for its huge concentration of fossilized
dinosaur tracks
