by Alex Gugel , all rights reserved
Bryce CanyonGeology |
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Bryce Canyon
National Park Service
U.S. Department of the Interior
Bryce Canyon National Park
The Story in the Rocks
The geology of Bryce Canyon is a story rich with change and the exciting interaction
between nature’s forces. The creation of the unique landscape that makes Bryce
Canyon famous began between 35 and 55 million years ago, when much of southern
Utah was covered by braided rivers and streams, and later by a system of lakes.
However, the story really begins millions of years before.
The Top of the Stairs
In the preface to Clarence E Dutton’s Report on
the Geology of the High Plateaus of Utah (1880),
John Wesley Powell wrote “These cliffs are bold
escarpments hundreds and thousands of feet
in altitude - grand steps by which the region is
terraced.” Powell was describing a series of cliffs
we now know as the Grand Staircase, visible from
the Kaibab Plateau north of the Grand Canyon.
Each of Powell’s steps represents a different
period of geologic history, beginning 260 million
years ago in the Permian. A low lying set of cliffs
of Lower Triassic-aged marine sediments make
up the first riser in the staircase, the Chocolate
Cliffs. The Vermilion Cliffs are the second step
and consist of Middle to Upper Triassic marine,
river, and swamp sediments. The third step has its
origins in a vast desert from the Lower Jurassic,
larger than the present day Sahara, known as
the White Cliffs and dominated by the Navajo
Sandstone formation.
The oldest rocks exposed at Bryce Canyon are
from the Lower Cretaceous, when most of North
America was under water. The Dakota Formation,
Tropic Shale, and Straight Cliffs Formation are
marine sediments associated with the Western
Interior Seaway. These rock layers, along with
the slightly younger Wahweap Formation, are
the Gray Cliffs, covering a span of time from 100
to 75 million years ago, are the fourth step in the
staircase. The Pink Cliffs of the Claron Formation
are the fifth and final step.
Setting the Scene
One of the most significant factors in the creation
of many of the landscapes seen in western North
America is the subduction of the Pacific Oceanic
Plate (originally the Kula and Farallon Plates)
beneath the North American Continental Plate.
For millions of years the western portion of the
continent had been at or below sea level, and the
forces of this ongoing collision between plates are
responsible for the west’s higher elevations that
exist today. Beginning in the middle to late Jurassic
a mountain building event took place, the Sevier
Orogeny, in what is now eastern Nevada and
western Utah. As this period of uplift was winding
down, interaction between the plates continued
and the Laramide Orogeny began during the
Cretaceous, uplifting the mountain chain we call
the Rockies. Between these mountain ranges a
large basin formed, creating a perfect place for
snowmelt and rain runoff to collect.
Watery Beginnings
With well formed mountain ranges lying to the
west and east, rivers and streams flowed into
the basin below and, from what is now southern
Utah up to Wyoming, a chain of lakes formed.
The southernmost of these lakes has been named
Lake Claron, the name having been derived from
a mountain in western Utah - Mount Claron where the Claron Formation was first described
(in geologic terms, the type locality). Water is one
of the most powerful forces on Earth, and as rain
fell and snow melted, it began to take apart those
mountain ranges, grain by grain. These grains
became the sediments that would collect on the
lake’s bottom.
Pink Cliffs
Gray Cliffs
White Cliffs
Vermilion Cliffs
Four of the Grand Staircase’s five steps
Early on, as water first began to flow into the
basin, what existed here was probably more
marsh-like than an actual lake. Silts and muds
were carried into the basin by the rivers and
streams, along with minerals like iron and
manganese. The roots of plants living in this
marsh help to oxidize these minerals, contributing
to the spectacular colors visible today. The Lower
Pink Member of the Claron Formation gets its
Watery Beginnings
(continued)
distinctive pink color from iron oxides, with veins
of dark blue to purple caused by manganese
oxides. In addition, the waters were also rich in
calcium carbonate, which comes from dissolved
limestone and, once the sediments dry out,
becomes the glue that bonds the grains together,
forming rock.
Within the Pink Member there are also thin layers
of gray rock that are not continuous, suggesting
there were periods where this marshy landscape
had dried and was instead dotted with many
ponds. Indications are that these ponds were salty
or highly mineralized, with nothing able to survive
in them except cyanobacteria (blue-green algae).
By enriching the sediments with magnesium the
algae extracted from the water, they helped to
create dolostone, an important piece of the puzzle
in the formation of hoodoos.
Utah region 50 million years ago. Sediment eroded
from mountains in Northwestern Utah was deposited
in a lake and lithified (turned to stone).
Later, as the basin began to fill, a large lake with
fresher water appears to have formed. The Upper
White Member of the Claron Formation is not
iron-rich like the Lower Pink Member and lacks
the distinctive color.
Geologists are not certain exactly when the
lake, ponds, and marshes were here, but can
date the underlying and overlying layers with
great precision. Around 55 million years ago the
Claron Basin began to fill and, by 35 mya, the lake
disappeared. While rocks can tell many stories,
one left untold is whether Lake Claron drained
out of the basin, or it simply dried up. That part of
the geologic record eroded away, and has left the
question unanswered.
Uplifting Experiences
With the lake dry and sediments solidifying to
become rock, another event must take place
before hoodoos can begin to form. Around 15 Mya
the same plate tectonics responsible for mountain
building begin to act on the land. Over the next
10 million years the land would rise nearly a
vertical mile, creating the 140,000 square mile
Colorado Plateau. In this portion of the Colorado
Plateau the underlying bedrock would break
and form deep faults that split the plateau apart,
creating seven blocks separated by these faults.
As the tectonic forces that were pushing up the
Colorado Plateau continued to act, these seven
blocks were pushed up even further, creating
Utah’s High Plateaus Region. One of these blocks
became what we call the Pausaugunt Plateau, and
it is along this plateau’s eastern edge that Bryce
Canyon is being formed.
How to Make a Hoodoo
The Paria River and its tributaries have eroded
away several thousand feet of bedrock between
Bryce Canyon and the Table Cliff, 15 miles to the
east, exposing the rocks of the Gray Cliffs that lie
below. Running parallel along the eastern edge of
the park boundary is the Paunsaugunt Fault, and
the colorful hoodoos and badlands that make the
park famous are being formed as the plateau’s
edge erodes westward from this fault.
openings in the fins called ice windows. As the
seasons come and go, these windows eventually
become so large that the top of the window
collapses – along with its protective layer of
harder dolomitic limestone. Additional windows
form in the fin and also ultimately collapse
until the long, flat topped fin becomes a row of
hoodoos. Most hoodoos are still capped by this
protective layer of dolomitic limestone, helping to
preserve them for thousands of years.
All Good Things Must
Come to an End
During periods of uplift, earthquakes created
fractures and joints within the bedrock. More than
200 days each year temperatures at Bryce Canyon
rise above freezing during the day, then drop to
well below freezing at night. With annual snowfall
totals of up to 8 ft./2.6 m, snow will melt and find
its way into those fractures and joints. When the
melted snow refreezes at night, the ice begins to
break the rock apart. Summer monsoonal rains
then carry away the debris. The rain also eats away
at the plateau’s edge until it encounters one of the
harder dolomitic limestone layers. Rather than
carry this rock away, it flows around this layer,
eventually forming a fin. Within these fins, freezethaw cycles continue to carve the rock, forming
An ice window (circled) has formed along a joint in a
fin near Sunset Point; to the left is a collapsed window
along another joint - the beginnings of a new hoodoo.
The relentless force of water never stops carving
away at the Claron Formation. Each year many
tons of rock are cracked and broken away during
the winter, then the summer monsoons dissolve
the calcite bonding them together. The Paria
River and its tributaries carry these sediments
to the Colorado River, where they will become
new sedimentary layers down river. The eastern
edge of the Pausaugunt Plateau marches steadily
toward the East Fork of the Sevier River, currently
draining the upper reaches of the plateau. In
approximately 3 million years the plateau’s edge
will breech the river, its waters carrying away what
remains of Bryce Canyon in a relatively short
period of geologic time. The water will then begin
to attack the Gray Cliffs that lie below, the next
victim in the never ending cycle of deposition and
erosion.
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