The exposed geology of the Bryce Canyon area in
Utah
Utah ( , ) is a state in the Mountain West subregion of the Western United States. Utah is a landlocked U.S. state bordered to its east by Colorado, to its northeast by Wyoming, to its north by Idaho, to its south by Arizona, and to it ...
shows a record of deposition that covers the last part of the
Cretaceous
The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of ...
Period
Period may refer to:
Common uses
* Era, a length or span of time
* Full stop (or period), a punctuation mark
Arts, entertainment, and media
* Period (music), a concept in musical composition
* Periodic sentence (or rhetorical period), a concept ...
and the first half of the
Cenozoic era in that part of
North America. The ancient
depositional environment
In geology, depositional environment or sedimentary environment describes the combination of physical, chemical, and biological processes associated with the deposition of a particular type of sediment and, therefore, the rock types that will be ...
of the region around what is now
Bryce Canyon National Park
Bryce Canyon National Park () is an American national park located in southwestern Utah. The major feature of the park is Bryce Canyon, which despite its name, is not a canyon, but a collection of giant natural amphitheaters along the eastern ...
varied from the warm shallow sea (called the
Cretaceous Seaway) in which the Dakota Sandstone and the Tropic Shale were deposited to the cool
streams and
lake
A lake is an area filled with water, localized in a basin, surrounded by land, and distinct from any river or other outlet that serves to feed or drain the lake. Lakes lie on land and are not part of the ocean, although, like the much large ...
s that contributed sediment to the colorful Claron Formation that dominates the park's amphitheaters.
Other formations were also formed but were mostly
eroded
Erosion is the action of surface processes (such as water flow or wind) that removes soil, rock, or dissolved material from one location on the Earth's crust, and then transports it to another location where it is deposited. Erosion is disti ...
following uplift from the
Laramide orogeny
The Laramide orogeny was a time period of mountain building in western North America, which started in the Late Cretaceous, 70 to 80 million years ago, and ended 35 to 55 million years ago. The exact duration and ages of beginning and end of the ...
which started around 70
million years ago
The abbreviation Myr, "million years", is a unit of a quantity of (i.e. ) years, or 31.556926 teraseconds.
Usage
Myr (million years) is in common use in fields such as Earth science and cosmology. Myr is also used with Mya (million years ago) ...
(
mya). This event raised the
Rocky Mountains
The Rocky Mountains, also known as the Rockies, are a major mountain range and the largest mountain system in North America. The Rocky Mountains stretch in straight-line distance from the northernmost part of western Canada, to New Mexico ...
far to the east and caused the retreat of the sea that covered the Bryce Canyon area. After Laramide mountain building came to an end, about 15 mya, a large part of western North America began to be stretched into the nearby
Basin and Range
Basin and range topography is characterized by alternating parallel mountain ranges and valleys. It is a result of crustal extension due to mantle upwelling, gravitational collapse, crustal thickening, or relaxation of confining stresses. The e ...
topography. The greater Bryce area was uplifted as part of the High Plateaus by the same forces. Uplift of the
Colorado Plateaus and the opening of the
Gulf of California
The Gulf of California ( es, Golfo de California), also known as the Sea of Cortés (''Mar de Cortés'') or Sea of Cortez, or less commonly as the Vermilion Sea (''Mar Bermejo''), is a marginal sea of the Pacific Ocean that separates the Baja C ...
by 5 mya changed the drainage of the
Colorado River
The Colorado River ( es, Río Colorado) is one of the principal rivers (along with the Rio Grande) in the Southwestern United States and northern Mexico. The river drains an expansive, arid watershed that encompasses parts of seven U.S. s ...
and its tributaries, including the
Paria River
The Paria River is a tributary of the Colorado River, approximately long, in southern Utah and northern Arizona in the United States. It drains a rugged and arid region northwest of the Colorado, flowing through roadless slot canyons along part ...
, which is eroding headward between two plateaus adjacent to the park. The uplift caused the formation of vertical joints which were later preferentially eroded to form the free-standing pinnacles called
hoodoos,
badland
Badlands are a type of dry terrain where softer sedimentary rocks and clay-rich soils have been extensively eroded."Badlands" in ''Chambers's Encyclopædia''. London: George Newnes, 1961, Vol. 2, p. 47. They are characterized by steep slopes, m ...
s, and
monolith
A monolith is a geological feature consisting of a single massive stone or rock, such as some mountains. For instance, Savandurga mountain is a monolith mountain in India. Erosion usually exposes the geological formations, which are often ma ...
s we see today.
The formations exposed in the area of the park are part of the
Grand Staircase. The oldest members of this supersequence of rock units are exposed in the
Grand Canyon, the intermediate ones in
Zion National Park
Zion National Park is an American national park located in southwestern Utah near the town of Springdale. Located at the junction of the Colorado Plateau, Great Basin, and Mojave Desert regions, the park has a unique geography and a variety of ...
, and its youngest parts are laid bare in Bryce Canyon area. A small amount of overlap occurs in and around each park.
Grand Staircase
The
rocks exposed in Bryce Canyon are about 100 million years younger than those in nearby
Zion National Park
Zion National Park is an American national park located in southwestern Utah near the town of Springdale. Located at the junction of the Colorado Plateau, Great Basin, and Mojave Desert regions, the park has a unique geography and a variety of ...
, and the rocks exposed in Zion are younger than those in the
Grand Canyon to the south.
There are, however, shared rock units between all three, creating a supersequence of
formations that geologists call the Grand Staircase. Together the formations of the Grand Staircase record nearly 2000 million years of the
Earth
Earth is the third planet from the Sun and the only astronomical object known to harbor life. While large volumes of water can be found throughout the Solar System, only Earth sustains liquid surface water. About 71% of Earth's surfa ...
's history. Bryce Canyon's formations are the youngest known units in the Grand Staircase. Younger rock units, if they ever existed, have been removed by
erosion
Erosion is the action of surface processes (such as water flow or wind) that removes soil, rock, or dissolved material from one location on the Earth's crust, and then transports it to another location where it is deposited. Erosion is dis ...
.
Cretaceous Seaway
Advance
In the
Cretaceous
The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of ...
, a shallow seaway spread into the interior of
North America from the
Gulf of Mexico
The Gulf of Mexico ( es, Golfo de México) is an ocean basin and a marginal sea of the Atlantic Ocean, largely surrounded by the North American continent. It is bounded on the northeast, north and northwest by the Gulf Coast of the United ...
in the south into
Utah
Utah ( , ) is a state in the Mountain West subregion of the Western United States. Utah is a landlocked U.S. state bordered to its east by Colorado, to its northeast by Wyoming, to its north by Idaho, to its south by Arizona, and to it ...
and later to the
Arctic Ocean
The Arctic Ocean is the smallest and shallowest of the world's five major oceans. It spans an area of approximately and is known as the coldest of all the oceans. The International Hydrographic Organization (IHO) recognizes it as an ocean, a ...
in the far north.
[Davis and Pollock (2003). ''Geology of Bryce Canyon National Park'', page 45] Geologists call this shallow sea the
Cretaceous Seaway or Western Interior Seaway. The seaway divided North America into two halves: an eastern portion dominated by the already ancient
Appalachian Mountains
The Appalachian Mountains, often called the Appalachians, (french: Appalaches), are a system of mountains in eastern to northeastern North America. The Appalachians first formed roughly 480 million years ago during the Ordovician Period. They ...
and a western part composed primarily of the still growing Sevier Mountains;
formed from shallow
thrust fault
A thrust fault is a break in the Earth's crust, across which older rocks are pushed above younger rocks.
Thrust geometry and nomenclature
Reverse faults
A thrust fault is a type of reverse fault that has a dip of 45 degrees or less.
If ...
ing caused by the
Sevier orogeny
The Sevier orogeny was a mountain-building event that affected western North America from northern Canada to the north to Mexico to the south.
The Sevier orogeny was the result of convergent boundary tectonic activity, and deformation occurred f ...
.
[Davis and Pollock (2003). ''Geology of Bryce Canyon National Park'', page 55] As the shoreline moved back and forth, the Bryce area alternated from being part of the Sevier landmass to being under the Cretaceous Seaway. Alternating layers of nonmarine, intertidal, and marine sediments lay on top of each other as a result.
Conglomerate,
siltstone, and
fossil
A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved ...
-rich
sandstone
Sandstone is a clastic sedimentary rock composed mainly of sand-sized (0.0625 to 2 mm) silicate grains. Sandstones comprise about 20–25% of all sedimentary rocks.
Most sandstone is composed of quartz or feldspar (both silicates ...
that together are up to thick mark the arrival of the Cretaceous Seaway.
Called the
Dakota Sandstone
The Dakota is a sedimentary geologic unit name of formation and group rank in Midwestern North America. The Dakota units are generally composed of sandstones, mudstones, clays, and shales deposited in the Mid-Cretaceous opening of the Western ...
, it is the oldest
formation exposed in the Bryce Canyon area but the youngest one exposed in the Zion and Kolob canyons area to the southwest. Abundant amounts of
petrified wood
Petrified wood, also known as petrified tree (from Ancient Greek meaning 'rock' or 'stone'; literally 'wood turned into stone'), is the name given to a special type of '' fossilized wood'', the fossilized remains of terrestrial vegetation. ' ...
,
oyster
Oyster is the common name for a number of different families of salt-water bivalve molluscs that live in marine or brackish habitats. In some species, the valves are highly calcified, and many are somewhat irregular in shape. Many, but not ...
beds containing millions of fossils, and
coal
Coal is a combustible black or brownish-black sedimentary rock, formed as rock strata called coal seams. Coal is mostly carbon with variable amounts of other elements, chiefly hydrogen, sulfur, oxygen, and nitrogen.
Coal is formed when ...
are all found in the Dakota.
In the Bryce Canyon area, this formation can be seen in the
Paria Valley where it is found as a lithified blanket
sand
Sand is a granular material composed of finely divided mineral particles. Sand has various compositions but is defined by its grain size. Sand grains are smaller than gravel and coarser than silt. Sand can also refer to a textural class o ...
that probably accumulated on
beach
A beach is a landform alongside a body of water which consists of loose particles. The particles composing a beach are typically made from rock, such as sand, gravel, shingle, pebbles, etc., or biological sources, such as mollusc sh ...
es, in
lagoon
A lagoon is a shallow body of water separated from a larger body of water by a narrow landform, such as reefs, barrier islands, barrier peninsulas, or isthmuses. Lagoons are commonly divided into ''coastal lagoons'' (or ''barrier lagoons'') ...
s, and vast coal-producing
swamps as the Cretaceous Seaway transgressed (advanced inland) over the region and later retreated.
[Harris, Ann (1997). ''Geology of National Parks'', page 51] It sits unconformably on much older
Jurassic
The Jurassic ( ) is a geologic period and stratigraphic system that spanned from the end of the Triassic Period million years ago (Mya) to the beginning of the Cretaceous Period, approximately Mya. The Jurassic constitutes the middle period of ...
formations that are not exposed in the immediate area (see
geology of the Zion and Kolob canyons area
The geology of the Zion and Kolob canyons area includes nine known exposed formations, all visible in Zion National Park in the U.S. state of Utah. Together, these formations represent about 150 million years of mostly Mesozoic-aged sediment ...
for a discussion about these older sediments).
Mud and
silt
Silt is granular material of a size between sand and clay and composed mostly of broken grains of quartz. Silt may occur as a soil (often mixed with sand or clay) or as sediment mixed in suspension with water. Silt usually has a floury feel ...
were deposited on top of the Dakota Formation as the seaway became deeper and calmer in the area.
The resulting dark gray to black
Tropic Shale
The Tropic Shale is a Mesozoic geologic formation. Dinosaur remains are among the fossils that have been recovered from the formation,Weishampel, ''et al.'' (2004). "Dinosaur distribution." Pp. 517-607. including '' Nothronychus graffami''.
The Tr ...
records the maximum transgression of the seaway into Utah and is thick in the Paria Amphitheater.
It forms the unvegetated badlands seen in the
Tropic Valley and is perhaps the most fossil-rich formation in the area; containing numerous straight-shelled and coiled
ammonites.
Retreat
The Cretaceous Seaway was already retreating east and to the south by the time the locally thick
Straight Cliffs Formation
The Straight Cliffs Formation is a stratigraphic unit in the Kaiparowits Plateau of south central Utah. It is Late Cretaceous (latest Turonian – early Campanian) in age and contains fluvial (river systems), paralic (swamps and lagoons), and marg ...
was deposited.
[Davis and Pollock (2003). ''Geology of Bryce Canyon National Park'', page 46] Its
members
Member may refer to:
* Military jury, referred to as "Members" in military jargon
* Element (mathematics), an object that belongs to a mathematical set
* In object-oriented programming, a member of a class
** Field (computer science), entries in ...
represent various stages in this process. The cliff-forming sandstone of the Tibbet Canyon Member was conformably deposited on top of the Tropic Shale in shallow marine and later near shore environments. Shale and sandstone from the Smoky Hollow Member were deposited on top of its basal layer of coal-rich mudstone in coastal swamps and lagoons on the shore of the seaway. While the alternating layers of shale and sandstone mixed with massive coal deposits of the John Henry Member were laid down in swamps, lagoons and
fluvial environments, one member, the Drip Tank, is not found in the Bryce Canyon area.
This formation erodes into almost unclimbable cliffs and escarpments of whitish to yellow-gray sandstones with comparatively thin interbedded layers of shale and mudstone.
Shark teeth
Sharks continually shed their teeth; some Carcharhiniformes shed approximately 35,000 teeth in a lifetime, replacing those that fall out. There are four basic types of shark teeth: dense flattened, needle-like, pointed lower with triangular upp ...
are found in the lower parts of the formation.
Lakes and east-flowing rivers became the dominant resting place for sediment following the retreat of the Cretaceous Seaway. The shales and sandstones of the locally thick
Wahweap Formation
The Wahweap Formation of the Grand Staircase–Escalante National Monument is a geological formation in southern Utah and northern Arizona, around the Lake Powell region, whose strata date back to the Late Cretaceous (Campanian stage). Dinosaur r ...
were deposited in moving water (fluvial setting).
This formation is part of the Grey Cliffs of the Grand Staircase mentioned previously. It contains abundant fossils of
vertebrate
Vertebrates () comprise all animal taxa within the subphylum Vertebrata () (chordates with backbones), including all mammals, birds, reptiles, amphibians, and fish. Vertebrates represent the overwhelming majority of the phylum Chordata, with c ...
s, including
dinosaur
Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the evolution of dinosaurs is t ...
s such as the
hadrosaur
Hadrosaurids (), or duck-billed dinosaurs, are members of the ornithischian family Hadrosauridae. This group is known as the duck-billed dinosaurs for the flat duck-bill appearance of the bones in their snouts. The ornithopod family, which incl ...
s.
Continental deposition
Flood plains uplift and erode
A
flood plain crossed by rivers and lakes developed in the area. Mud and sand accumulated in this setting to become the gray sandstones and mudstones of the
Kaiparowits Formation
The Kaiparowits Formation is a sedimentary rock formation found in the Kaiparowits Plateau in Grand Staircase–Escalante National Monument, in the southern part of Utah in the western United States. It is over 2800 feet (850 m) thick, and is ...
. This formation is up to thick in the Bryce Canyon area, but other parts of the Kaiparowits in the region are several hundreds of feet (tens of meters) thick.
Two formations, the
Canaan Peak and the
Pine Hollow, sit on top of the Kaiparowits elsewhere in the region but are absent in the Bryce Canyon area. The sandstones and conglomerates of these formations record stream and river deposition starting in the
Paleocene
The Paleocene, ( ) or Palaeocene, is a geological epoch that lasted from about 66 to 56 million years ago (mya). It is the first epoch of the Paleogene Period in the modern Cenozoic Era. The name is a combination of the Ancient Greek ''pal ...
epoch.
Uplift caused by a
mountain
A mountain is an elevated portion of the Earth's crust, generally with steep sides that show significant exposed bedrock. Although definitions vary, a mountain may differ from a plateau in having a limited summit area, and is usually highe ...
-building episode called the
Laramide orogeny
The Laramide orogeny was a time period of mountain building in western North America, which started in the Late Cretaceous, 70 to 80 million years ago, and ended 35 to 55 million years ago. The exact duration and ages of beginning and end of the ...
lasted from the late Cretaceous around 70 mya to the early Paleocene. This hoisted the once lower uplands skyward while low-lying
basins between them gradually subsided.
[Harris, Ann (1997). ''Geology of National Parks'', page 52] Compression from the Laramide event deformed the land in the area to form the up to 5° dipping Bryce Canyon Anticline. All of the Canaan Peak, Pine Hollow, Kaiparowits, and Waheap formations, along with part of the underlying Straight Cliffs, were removed from the anticline's crest by erosion before the Claron Formation was deposited.
[Davis and Pollock (2003). ''Geology of Bryce Canyon National Park'', page 53] An
angular unconformity
An unconformity is a buried erosional or non-depositional surface separating two rock masses or strata of different ages, indicating that sediment deposition was not continuous. In general, the older layer was exposed to erosion for an interval ...
therefore exists along the anticline's crest. The park also sits on the western gently dipping flank of the much larger
Kaibab uplift, which was also formed as a result of the Laramide.
Claron flood plain and lake system
Uplift from the Laramide paused briefly in the
Eocene
The Eocene ( ) Epoch is a geological epoch that lasted from about 56 to 33.9 million years ago (mya). It is the second epoch of the Paleogene Period in the modern Cenozoic Era. The name ''Eocene'' comes from the Ancient Greek (''ēṓs'', " ...
.
Meandering streams flowed slowly over the resulting broad and almost featureless plains. Periodic but extensive
flood
A flood is an overflow of water ( or rarely other fluids) that submerges land that is usually dry. In the sense of "flowing water", the word may also be applied to the inflow of the tide. Floods are an area of study of the discipline hydrol ...
s inundated large areas perhaps once every 1,000 years; spreading mud, cobbles and fine silt over the plains.
Erosion
Erosion is the action of surface processes (such as water flow or wind) that removes soil, rock, or dissolved material from one location on the Earth's crust, and then transports it to another location where it is deposited. Erosion is dis ...
incised these deposits between flood events and
plant
Plants are predominantly photosynthetic eukaryotes of the kingdom Plantae. Historically, the plant kingdom encompassed all living things that were not animals, and included algae and fungi; however, all current definitions of Plantae exclu ...
growth was abundant. Oxidation of the
iron
Iron () is a chemical element with Symbol (chemistry), symbol Fe (from la, Wikt:ferrum, ferrum) and atomic number 26. It is a metal that belongs to the first transition series and group 8 element, group 8 of the periodic table. It is, Abundanc ...
in the mud and silt turned the soil into
hematite, giving it a pink and red hue. These sediments were later lithified into the up-to- -thick Pink Member of the locally Eocene-aged Claron Formation (previously called the Wasatch Formation).
Channelized conglomerates of this member can be easily seen in Red Canyon along
State Route 12 while its silt and mudstones compose most of the park's fragile and colorful spires called
hoodoos. Geologist
Clarence Dutton
Clarence Edward Dutton (May 15, 1841 – January 4, 1912) was an American geologist and US Army officer. Dutton was born in Wallingford, Connecticut on May 15, 1841. He graduated from Yale College in 1860 and took postgraduate courses there until ...
called the
iron oxide-rich lower member of the Claron the
Pink Cliffs series due to its colorful appearance.
A large system of shallow but expansive
lake
A lake is an area filled with water, localized in a basin, surrounded by land, and distinct from any river or other outlet that serves to feed or drain the lake. Lakes lie on land and are not part of the ocean, although, like the much large ...
s and associated
deltas covered several thousand square miles of what is now northwest
Colorado
Colorado (, other variants) is a state in the Mountain states, Mountain West subregion of the Western United States. It encompasses most of the Southern Rocky Mountains, as well as the northeastern portion of the Colorado Plateau and the wes ...
and southwest
Utah
Utah ( , ) is a state in the Mountain West subregion of the Western United States. Utah is a landlocked U.S. state bordered to its east by Colorado, to its northeast by Wyoming, to its north by Idaho, to its south by Arizona, and to it ...
and
Wyoming
Wyoming () is a state in the Mountain West subregion of the Western United States. It is bordered by Montana to the north and northwest, South Dakota and Nebraska to the east, Idaho to the west, Utah to the southwest, and Colorado to the s ...
.
These lakes existed from the Paleocene to mid
Oligocene but did not spread to the Bryce Canyon area until Eocene time.
Large quantities of lakebed sediments were laid down in this system during the 20 million years of its existence from about 60 to 40 mya.
[Kiver and Harris (1999). ''Geology of U.S. Parklands'', page 525] Climate change
In common usage, climate change describes global warming—the ongoing increase in global average temperature—and its effects on Earth's climate system. Climate change in a broader sense also includes previous long-term changes to ...
and cycles caused the lakes in the system to expand and shrink through time. As they did so, they left beds of differing thickness and composition stacked atop one another;
*various sand and cobble deposits near shore,
*
calcium
Calcium is a chemical element with the symbol Ca and atomic number 20. As an alkaline earth metal, calcium is a reactive metal that forms a dark oxide-nitride layer when exposed to air. Its physical and chemical properties are most similar t ...
-poor muds further from shore,
*calcium-rich mud in deeper water, and
*pure limey oozes were deposited in the deepest waters.
The limey oozes and mud were later lithified into the limestone and interbedded siltstone of the up-to-300 foot (90 m)-thick White Member of the Claron.
This member erodes into white-colored
monolith
A monolith is a geological feature consisting of a single massive stone or rock, such as some mountains. For instance, Savandurga mountain is a monolith mountain in India. Erosion usually exposes the geological formations, which are often ma ...
s that are found only at the highest elevations of the
Paunsaugunt Plateau. Fossils are rare in the White Member and consist mainly of
freshwater snails and
clam
Clam is a common name for several kinds of bivalve molluscs. The word is often applied only to those that are edible and live as infauna, spending most of their lives halfway buried in the sand of the seafloor or riverbeds. Clams have two shel ...
s, indicating that the lakes supported little life.
Most arches and natural bridges in the park, including the famous
Natural Bridge
A natural arch, natural bridge, or (less commonly) rock arch is a natural landform where an arch has formed with an opening underneath. Natural arches commonly form where inland cliffs, coastal cliffs, fins or stacks are subject to erosion ...
, were carved from sandstone beds in the Claron.
Marysvale volcanics
A gap in the geologic record following deposition of the Claron Formation was interrupted 34 to 31 mya by eruptions from the nearby
Marysvale volcanic field, which is located northwest of the park.
Volcanic ash
Volcanic ash consists of fragments of rock, mineral crystals, and volcanic glass, created during volcanic eruptions and measuring less than 2 mm (0.079 inches) in diameter. The term volcanic ash is also often loosely used to refer ...
and
lava
Lava is molten or partially molten rock (magma) that has been expelled from the interior of a terrestrial planet (such as Earth) or a moon onto its surface. Lava may be erupted at a volcano or through a fracture in the crust, on land or un ...
from these flows are found less than from Bryce Canyon but at least some volcanic material was likely deposited directly in the park area only to be later removed by erosion.
Most of the activity at the Marysvale volcanic field occurred during three separate intervals; ~34–22 mya, 22–14 mya and 9–5 mya.
Dacite
Dacite () is a volcanic rock formed by rapid solidification of lava that is high in silica and low in alkali metal oxides. It has a fine-grained (aphanitic) to porphyritic texture and is intermediate in composition between andesite and rhyolite ...
s and
andesite
Andesite () is a volcanic rock of intermediate composition. In a general sense, it is the intermediate type between silica-poor basalt and silica-rich rhyolite. It is fine-grained (aphanitic) to porphyritic in texture, and is composed predo ...
s were erupted above an evolving
batholith in the first interval. Crystal-rich ash from the 27-million-year-old (myo) Three Creeks caldera, 24 myo Big John caldera and 23 myo Monroe Peak caldera hardened into
tuff
Tuff is a type of rock made of volcanic ash ejected from a vent during a volcanic eruption. Following ejection and deposition, the ash is lithified into a solid rock. Rock that contains greater than 75% ash is considered tuff, while rock ...
.
The second and third intervals saw eruptions of great quantities of
rhyolites.
Alkali-rich rhyolite erupted in the second interval from the 19 myo Mount Belknap caldera.
The Marysvale volcanic field collapsed under its own weight around 20 mya; likely due to weaknesses in the
evaporite
An evaporite () is a water- soluble sedimentary mineral deposit that results from concentration and crystallization by evaporation from an aqueous solution. There are two types of evaporite deposits: marine, which can also be described as ocean ...
s of the
Carmel Formation
The Carmel Formation is a geologic formation in the San Rafael Group that is spread across the U.S. states of Wyoming, Utah, Colorado, north east Arizona and New Mexico. Part of the Colorado Plateau, this formation was laid down in the Middle J ...
some below.
Folding and faulting of the Claron Formation from the collapse created Ruby's Inn thrust. A slight downwarp running east–west and perpendicular to the thrust motion called the Bryce syncline was also created.
Volcanic activity in the Marysvale and Bryce area ceased some 500,000 years ago.
Basalt
Basalt (; ) is an aphanitic (fine-grained) extrusive igneous rock formed from the rapid cooling of low-viscosity lava rich in magnesium and iron (mafic lava) exposed at or very near the surface of a rocky planet or moon. More than 90 ...
ic rocks of the same age can be seen along the Sevier Fault near the entrance to Red Canyon; the dark colored volcanic rocks have been displaced by the fault some and are now in direct contact with the much older Claron Formation.
[Kiver and Harris (1999). ''Geology of U.S. Parklands'', page 526]
Late Cenozoic tectonics
Formation of the High Plateaus
Younger rock units were laid down but were mostly removed by subsequent uplift-accelerated erosion. Outcrops of these formations can be found in the northern part of the park and in a few places on the plateau rim. Among these are the thick
Oligocene or
Miocene
The Miocene ( ) is the first epoch (geology), geological epoch of the Neogene Period and extends from about (Ma). The Miocene was named by Scottish geologist Charles Lyell; the name comes from the Greek words (', "less") and (', "new") and mea ...
-aged
Boat Mesa Conglomerate and the
Pliocene
The Pliocene ( ; also Pleiocene) is the epoch in the geologic time scale that extends from 5.333 million to 2.58[Pleistocene
The Pleistocene ( , often referred to as the ''Ice age'') is the geological epoch that lasted from about 2,580,000 to 11,700 years ago, spanning the Earth's most recent period of repeated glaciations. Before a change was finally confirmed in ...](_blank)
-aged
Sevier River Formation.
[Harris, Ann (1997). ''Geology of National Parks'', page 53] The Boat Mesa is made mostly of conglomerates with minor amounts of sandstone and some limestone from lakes, representing stream and overbank flood deposits.
The brownish-gray sandstone and gravels of the Sevier River Formation were laid down in valleys that were part of the ancestral
Sevier River
The Sevier River (pronounced "severe") is a -long river in the Great Basin of southwestern Utah in the United States. Originating west of Bryce Canyon National Park, the river flows north through a chain of high farming valleys and steep canyons ...
drainage system.
Around 15 mya in
Miocene
The Miocene ( ) is the first epoch (geology), geological epoch of the Neogene Period and extends from about (Ma). The Miocene was named by Scottish geologist Charles Lyell; the name comes from the Greek words (', "less") and (', "new") and mea ...
time, tensional forces in
Nevada
Nevada ( ; ) is a state in the Western region of the United States. It is bordered by Oregon to the northwest, Idaho to the northeast, California to the west, Arizona to the southeast, and Utah to the east. Nevada is the 7th-most extensive, ...
to the west were so great that the crust was spread thin, creating the
Basin and Range Province
The Basin and Range Province is a vast physiographic region covering much of the inland Western United States and northwestern Mexico. It is defined by unique basin and range topography, characterized by abrupt changes in elevation, alternating ...
.
These same forces segmented what is now the western part of the
Colorado Plateau into nine different smaller plateaus, including the
Paunsaugunt that the park sits astride.
[Harris, Ann (1997). ''Geology of National Parks'', page 54][Kiver and Harris (1999). ''Geology of U.S. Parklands'', page 524] Long, north–south-trending normal
faults were either newly created or reactivated from older pre-existing faults; a plateau rose on one side of each fault while valleys subsided on the other as the crust was extended in an east–west direction.
Two of these faults bound the Paunsaugunt Plateau; the Sevier on the west and the Paunsaugunt on the east. Movement along these two faults has displaced the Claron Formation by 2,000 feet (600 m) relative to the Paria and Sevier valleys.
The
Hurricane Fault
The Hurricane Fault is an intracrustal seismic fault that runs along the boundary between the Colorado Plateau block and the Basin and Range geologic province of western North America. It is a 250-km-long, north-south striking, high-angle, down ...
marks the west edge of the
Markagunt Plateau
Markagunt Plateau is a volcanic field in southern Utah, United States. Formed in a region of older volcanics, it consists of several cinder cones and associated lava flows. Some of the lava flows feature lava tubes such as Mammoth Cave, while oth ...
and is the topographic boundary between the Basin and Range and the Colorado Plateaus provinces.
Cedar Breaks National Monument
Cedar Breaks National Monument is a U.S. National Monument located in the U.S. state of Utah near Cedar City. Cedar Breaks is a natural amphitheater, stretching across , with a depth of over . The elevation of the rim of the amphitheater is over ...
, which shares almost the same exposed geology and erosional features as Bryce Canyon National Park, sits on the west edge of the Markagunt.
The entire Colorado Plateau then started to uplift from near
sea level
Mean sea level (MSL, often shortened to sea level) is an average surface level of one or more among Earth's coastal bodies of water from which heights such as elevation may be measured. The global MSL is a type of vertical datuma standardise ...
to several thousand feet (over a kilometer) in elevation.
An alternate theory is that the Laramide orogeny uplifted what is today the Basin and Range and the Colorado Plateau and that the tensional forces that formed the Basin and Range caused that region to subside relative to the Colorado Plateau.
Whatever the order of events were, the High Plateaus region of the Colorado Plateau were by now nearly complete.
Modern drainage and erosion
Drainage of the Colorado Plateau was significantly altered by the opening of the
Gulf of California
The Gulf of California ( es, Golfo de California), also known as the Sea of Cortés (''Mar de Cortés'') or Sea of Cortez, or less commonly as the Vermilion Sea (''Mar Bermejo''), is a marginal sea of the Pacific Ocean that separates the Baja C ...
.
Rift
In geology, a rift is a linear zone where the lithosphere is being pulled apart and is an example of extensional tectonics.
Typical rift features are a central linear downfaulted depression, called a graben, or more commonly a half-grabe ...
ing tore
Baja California Peninsula northwestward from the
Mexican mainland starting some 10 to 5 mya.
The ancestral
Colorado River
The Colorado River ( es, Río Colorado) is one of the principal rivers (along with the Rio Grande) in the Southwestern United States and northern Mexico. The river drains an expansive, arid watershed that encompasses parts of seven U.S. s ...
responded to the regional downwarping by taking a shortcut to the sea by flowing into the new gulf. This significantly decreased the distance from the river's headwaters and its delta at the sea. Water in the Colorado and its tributaries moved faster as a result and cut down deeper, creating the canyonland topography.
Formation of approximately the current depth of the Colorado River's
Grand Canyon by 1.2 mya further caused its tributaries to cut down even deeper.
[Kiver and Harris (1999). ''Geology of U.S. Parklands'', page 407] Headward erosion
Headward erosion is erosion at the origin of a stream channel, which causes the origin to move back away from the direction of the stream flow, lengthening the stream channel.Essentials of Geology, 3rd Ed, Stephen Marshak It can also refer to ...
of one of those tributaries, the
Paria River
The Paria River is a tributary of the Colorado River, approximately long, in southern Utah and northern Arizona in the United States. It drains a rugged and arid region northwest of the Colorado, flowing through roadless slot canyons along part ...
, eroded north-northwestward toward what is now Paria Amphitheater.
[Davis and Pollock (2003). ''Geology of Bryce Canyon National Park'', page 56] The river took a route roughly parallel to and east of the Paunsaugunt Fault. Erosion from snow and rain that fall directly on the east-facing rim of the Paunsaugunt Plateau forms gullies that widen into alcoves and amphitheaters while differential erosion and
frost wedging create the
hoodoos. Streams on the plateau do not contribute to the formation of alcoves or amphitheaters because they flow away from the rim.
Erosion continues in this fashion today.
Hoodoo formation in Bryce Canyon
The Pink Member of the Claron Formation is largely composed of easily eroded and relatively soft limestone. When rain combines with
carbon dioxide
Carbon dioxide ( chemical formula ) is a chemical compound made up of molecules that each have one carbon atom covalently double bonded to two oxygen atoms. It is found in the gas state at room temperature. In the air, carbon dioxide is trans ...
it forms a weak solution of
carbonic acid. This acid helps to slowly dissolve the limestone in the Claron Formation grain by grain. It is this process of
chemical weathering
Weathering is the deterioration of rocks, soils and minerals as well as wood and artificial materials through contact with water, atmospheric gases, and biological organisms. Weathering occurs ''in situ'' (on site, with little or no movement ...
that rounds the edges of hoodoos and gives them their lumpy and bulging profiles.
In the winter, melting snow seeps into cracks and joints and freezes at night. The force of the expanding ice helps to erode the rock of the Claron Formation. Over 200 of these freeze/thaw cycles occur each year in Bryce Canyon.
[ (adapted public domain text)] Frost wedging exploits and widens the nearly vertical joint planes that divide the Pink Member of the Claron Formation.
Internal layers of mudstone, conglomerate and siltstone interrupt the limestone horizontally. These layers are more resistant to attack by carbonic acid and they can therefore act as protective capstones of fins, windows and hoodoos. Many of the more durable hoodoos are capped with a type of
magnesium
Magnesium is a chemical element with the symbol Mg and atomic number 12. It is a shiny gray metal having a low density, low melting point and high chemical reactivity. Like the other alkaline earth metals (group 2 of the periodic ta ...
-rich limestone called
dolomite Dolomite may refer to:
*Dolomite (mineral), a carbonate mineral
*Dolomite (rock), also known as dolostone, a sedimentary carbonate rock
*Dolomite, Alabama, United States, an unincorporated community
*Dolomite, California, United States, an unincor ...
.
Dolomite dissolves at a much slower rate, and consequently protects the weaker limestone underneath.
However, the same processes that create hoodoos will also eventually destroy them. In the case of Bryce Canyon, the hoodoos' rate of erosion is 2–4 feet (0.6–1.3 m) every 100 years.
As the canyon continues to erode to the west it will eventually capture (in perhaps 3 million years) the watershed of the East Fork of the
Sevier River
The Sevier River (pronounced "severe") is a -long river in the Great Basin of southwestern Utah in the United States. Originating west of Bryce Canyon National Park, the river flows north through a chain of high farming valleys and steep canyons ...
. Once this river flows through Bryce Amphitheater it will dominate the erosional pattern; replacing hoodoos with a V-shaped canyon and steep cliff walls typical of the weathering and erosional patterns created by rivers. A foreshadowing of this can be observed in Water Canyon while hiking the Mossy Cave Trail. A diversion canal has been taking a portion of the East Fork of the Sevier River through this section of the park for over 100 years.
Notes
References
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Further reading
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*{{cite book , title = Secrets in The Grand Canyon, Zion and Bryce Canyon National Parks , edition = Third , author = Tufts, Lorraine Salem , location = North Palm Beach, Florida , publisher = National Photographic Collections , year = 1998 , isbn = 0-9620255-3-4
*
Colorado Plateau
Bryce Canyon
Bryce Canyon National Park () is an American national park located in southwestern Utah. The major feature of the park is Bryce Canyon, which despite its name, is not a canyon, but a collection of giant natural amphitheaters along the eastern ...
Bryce Canyon
Bryce Canyon National Park () is an American national park located in southwestern Utah. The major feature of the park is Bryce Canyon, which despite its name, is not a canyon, but a collection of giant natural amphitheaters along the eastern ...