Geology of the Bryce Canyon area 643999 move=:edit= 218046094 2008-06-08T22:29:22Z Tillman 1663062 /* Flood plains uplift and erode */ correct wikilink, typo {{featured article}} The exposed '''geology of the Bryce Canyon area''' in [[Utah]] shows a record of deposition that covers the last part of the [[Cretaceous]] [[Period (geology)|Period]] and the first half of the [[Cenozoic]] era in that part of [[North America]]. The ancient depositional environment of the region around what is now [[Bryce Canyon National Park]] varied from the warm shallow sea (called the [[Cretaceous Seaway]]) in which the Dakota Sandstone and the Tropic Shale were deposited to the cool [[stream]]s and [[lakes]] that contributed sediment to the colorful Claron Formation that dominates the park's amphitheaters. Other formations were also formed but were mostly [[erosion|eroded]] following uplift from the [[Laramide orogeny]] which started around 70&nbsp;[[million years ago]] ([[mya (unit)|mya]]). This event created the [[Rocky Mountains]] far to the east and helped to close the sea that covered the area. A large part of western North America started to stretch itself into the nearby [[Basin and Range]] topography around 15&nbsp;mya. While not part of this region, the greater Bryce area was stretched into the High Plateaus by the same forces. Uplift of the [[Colorado Plateau]]s and the opening of the [[Gulf of California]] by 5&nbsp;mya changed the drainage of the [[Colorado River]] and its tributaries, including the [[Paria River]], which is eroding headward in between two plateaus adjacent to the park. The uplift caused vertical joints to form which were later preferentially eroded to form the free-standing pinnacles called [[hoodoo (geology)|hoodoo]]s, [[badland]]s, and [[monolith]]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]], and its youngest parts are laid bare in Bryce Canyon area. A small amount of overlap occurs in and around each park. [[Image:Paria View at Bryce Canyon NP.jpeg|thumb|350px|Paria View overlooks an intermittent stream flowing toward the [[Paria River]], some {{convert|8|mi|km|0}} to the east. About {{convert|2|mi|km|1}} away is the [[Paunsaugunt Fault]]; a normal fault along which the Paria River valley is subsiding on one side while the [[Paunsaugunt Plateau]] rises on the other. The pink-colored cliffs, alcoves and amphitheaters along the eroding eastern face of the plateau expose the approximately 50 million year old Claron Formation.]] ==Grand Staircase== {{main|Grand Staircase}} {{further information|[[geology of the Zion and Kolob canyons area]] and [[geology of the Grand Canyon area]]}} [[Image:Grand Staircase.jpg|thumb|250px|Grand Canyon (A), Chocolate Cliffs (B), Vermilion Cliffs (C), White Cliffs (D), Zion Canyon (E), Gray Cliffs (F), Pink Cliffs (G), Bryce Canyon (H)]] The [[rock (geology)|rocks]] exposed in Bryce Canyon are about 100 million years younger than those in nearby [[Zion National Park]], 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 [[formation (geology)|formations]] that geologists call the Grand Staircase. Together the formations of the Grand Staircase record nearly 2000 million years of the [[Earth]]'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]]. ==Cretaceous Seaway== ===Advance=== [[Image:Cretaceous Seaway.jpg|right|frame|<small>North America was divided by the [[Cretaceous Seaway]]</small>]] In the [[Cretaceous]] a shallow seaway spread into the interior of [[North America]] from the [[Gulf of Mexico]] in the south into [[Utah]] and later to the [[Arctic Ocean]] in the far north.<ref name="GBCNP45">Davis and Pollock (2003). ''Geology of Bryce Canyon National Park'', page 45</ref> Geologists call this shallow sea the [[Cretaceous Seaway]] or Western Interior Seaway. Whatever its name, the seaway divided North America into two halves; an eastern portion dominated by the already ancient [[Appalachian Mountains]] and a western part composed primarily of the still growing Sevier Mountains;<ref name="GBCNP45"/> formed from shallow [[thrust fault]]ing caused by the [[Sevier orogeny]].<ref name="GBCNP55">Davis and Pollock (2003). ''Geology of Bryce Canyon National Park'', page 55</ref> 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 (geology)|Conglomerate]], [[siltstone]], and [[fossil]]-rich [[sandstone]] that together are up to {{convert|300|ft|m|-1}} thick mark the arrival of the Cretaceous Seaway.<ref name="GBCNP45"/> Called the [[Dakota Sandstone]], it is the oldest [[formation (geology)|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]], [[oyster]] beds containing millions of fossils and [[coal]] are all found in the Dakota.<ref name="GBCNP45"/> In the Bryce Canyon area this formation can be seen in the [[Paria Valley]] where it is found as a lithified blanket [[sand]] that probably accumulated on [[beach]]es, in [[lagoon]]s, and vast coal-producing [[swamp]]s as the Cretaceous Seaway transgressed (advanced inland) over the region and later retreated.<ref name="GNP5th51">Harris, Ann (1997). ''Geology of National Parks'', page 51</ref> It sits uncomfortably on much older [[Jurassic]] formations that are not exposed in the immediate area (see [[geology of the Zion and Kolob canyons area]] for a discussion about these older sediments). [[Mud]] and [[silt]] were deposited on top of the Dakota Formation as the seaway became deeper and calmer in the area.<ref name="GNP5th51"/> The resulting dark gray to black [[Tropic Shale]] records the maximum transgression of the seaway into Utah and is {{convert|1000|ft|m|-1}} thick in the Paria Amphitheater.<ref name="GBCNP45"/> 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 [[ammonite]]s.<ref name="GBCNP45"/> ===Retreat=== The Cretaceous Seaway was already retreating east and to the south by the time the locally {{convert|1700|ft|m|-1}} thick [[Straight Cliffs Formation]] was deposited.<ref name="GBCNP46">Davis and Pollock (2003). ''Geology of Bryce Canyon National Park'', page 46</ref> Its [[member (geology)|members]] represent various stages in this process. The cliff-forming sandstone of the Tibbet Canyon Member was comfortably 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 other member, the Drip Tank, is not found in the Bryce Canyon area).<ref name="GBCNP46"/> 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]] are found in the lower parts of the formation.<ref name="GBCNP45"/> 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 {{convert|700|ft|m|-1}} thick [[Wahweap Formation]] were deposited in moving water (fluvial setting).<ref name="GBCNP46"/> This formation is part of the Grey Cliffs of the Grand Staircase mentioned previously. It contains abundant fossils of [[vertebrate]]s, including [[dinosaur]]s such as the [[hadrosaur]]s.<ref name="GBCNP45"/> ==Continental deposition== ===Flood plains uplift and erode=== [[Image:USA 10654 Bryce Canyon Luca Galuzzi 2007.jpg|thumb|[[Hoodoo (geology)|Hoodoos]] in Claron Formation, Bryce Canyon]] 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]]. This formation is up to {{convert|100|ft|m|-1}} thick in the Bryce Canyon area but other parts of the Kaiparowits in the region are hundreds of feet (tens of meters) thick.<ref name="GBCNP46"/> Two formations, the [[Canaan Peak Formation|Canaan Peak]] and the [[Pine Hollow Formation|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]]epoch.<ref name="GBCNP46"/> Uplift caused by a [[mountain]]-building episode called the [[Laramide orogeny]] lasted from the late Cretaceous around 70&nbsp;mya to the early Paleocene. This hoisted the once lower uplands skyward while low-lying [[Sedimentary basin|basins]] between them gradually subsided.<ref name="GNP5th52">Harris, Ann (1997). ''Geology of National Parks'', page 52</ref> 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.<ref name="GBCNP53">Davis and Pollock (2003). ''Geology of Bryce Canyon National Park'', page 53</ref> An [[angular unconformity]] 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.<ref name="GBCNP55"/> ===Claron flood plain and lake system=== Uplift from the Laramide paused briefly in the [[Eocene]].<ref name="GBCNP55"/> Meandering streams flowed slowly over the resulting broad and almost featureless plains. Periodic but extensive [[flood]]s inundated large areas perhaps once every 1,000 years; spreading mud, cobbles and fine silt over the plains.<ref name="GBCNP46"/> [[Erosion]] incised these deposits between flood events and [[plant]] growth was abundant. Oxidation of the [[iron]] 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 {{convert|700|ft|m|-1}} thick Pink Member of the locally Eocene-aged '''Claron Formation''' (previously called the Wasatch Formation).<ref name="GBCNP46"/> Channelized conglomerates of this member can be easily seen in Red Canyon along [[Utah State Route 12|State Route 12]] while its silt and mudstones compose most of the park's fragile and colorful spires called [[hoodoo (geology)|hoodoos]]. Geologist [[Clarence Dutton]] called the [[iron oxide]]-rich lower member of the Claron the [[Pink Cliffs]] series due to its colorful appearance.<ref name="GNP5th52"/> [[Image:Claron lake system.jpg|frame|right|Claron lake system]] A large system of shallow but expansive [[lake]]s and associated [[delta (landform)|deltas]] covered several thousand square miles of what is now northwest [[Colorado]] and southwest [[Utah]] and [[Wyoming]].<ref name="GUSP5th525"/> These lakes existed from the Paleocene to mid [[Oligocene]] but did not spread to the Bryce Canyon area until Eocene time.<ref name="GBCNP46"/> Large quantities of lakebed sediments were laid down in this system during the 20 million years of it existence from about 60 to 40&nbsp;mya.<ref name="GUSP5th525">Kiver and Harris (1999). ''Geology of U.S. Parklands'', page 525</ref> [[Climate change]] 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;<ref name="GNP5th52"/> *various sand and cobble deposits near shore, *[[calcium]]-poor muds further from shore, *calcium-rich mud in deeper water, and *pure limey oozes were deposited in the deepest waters. The limey ooses and mud were later lithified into the limestone and interbedded siltstone of the up to 300&nbsp;foot (90&nbsp;m) thick White Member of the Claron.<ref name="GBCNP46"/> This member erodes into white-colored [[monolith]]s that are only found at the highest elevations of the [[Paunsaugunt Plateau]]. Fossils are rare in the White Member and mainly consist of freshwater [[snail]]s and [[clam]]s, indicating that the lakes supported little life.<ref name="GBCNP46"/> Most arches and natural bridges in the park, including the famous [[Natural Bridges National Monument|Natural Bridge]], were carved from sandstone beds in the Claron. ===Marysvale volcanics=== <!-- NEEDS CITE AND CONTEXT Almost 25 million years of the geologic record is missing following the deposition of the Caron Formation. -->A gap in the geologic record following deposition of the Claron Formation was interrupted 34 to 31&nbsp;mya by eruptions from the nearby [[Marysvale volcanic field]], which is located northwest of the park.<ref name="USGS_Marysvale">{{cite book|url=http://geo-nsdi.er.usgs.gov/metadata/map-i/2645/a/metadata.faq.html#what | title=Geologic Map of the Central Marysvale Volcanic Field, Southwestern Utah|publisher=United States Geological Survey|accessdate=2007-08-12|last=Rowley|first=Peter D.|coauthors=Cunningham, Charles G.; Steven, Thomas A.; Workman, Jeremiah B.; Anderson, John J.; and Theissen, Kevin M.|date=2002|work=U.S. Geological Survey Geologic Investigations Series I-2645-A|location=Denver, Colorado}}</ref><ref name="Cunningham2002">{{cite web|url=http://gsa.confex.com/gsa/2002RM/finalprogram/abstract_33476.htm|title=Volcanic rocks and ore deposits of the Marysvale Volcanic Field, west-central Utah |last=Cunningham|first=Charles G.|accessdate=2007-08-12|date=2002|publisher=The Geological Society of America}}</ref> [[Volcanic ash]] and [[lava]] from these flows are found less than {{convert|20|mi|km|-1}} from Bryce Canyon but at least some volcanic material was likely deposited directly in the park area only to be later removed by erosion.<ref name="GBCNP55"/> Most of the activity at the Marysvale volcanic field occurred during three separate intervals; ~34&ndash;22&nbsp;mya, 22&ndash;14&nbsp;mya and 9&ndash;5&nbsp;mya.<ref name="Cunningham2002"/> [[Dacite]]s and [[andesite]]s were erupted above an evolving [[batholith]] in the first interval. Crystal-rich ash from the 27&nbsp;million year old (myo) Three Creeks caldera, 24&nbsp;myo Big John caldera and 23&nbsp;myo Monroe Peak caldera hardened into [[tuff]].<ref name="Cunningham2002"/> The second and third intervals saw eruptions of great quantities of [[rhyolite]]s. [[Alkali]]-rich rhyolite erupted in the second interval from the 19&nbsp;myo Mount Belknap caldera.<ref name="Cunningham2002"/> The Marysvale volcanic field collapsed under its own weight around 20&nbsp;mya; likely due to weaknesses in the [[evaporite]]s of the [[Carmel Formation]] some {{convert|5000|ft|m|-2}} below.<ref name="GBCNP55"/> 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.<ref name="GBCNP55"/> Volcanic activity in the Marysvale and Bryce area ceased some 500,000 years ago.<ref name="USGS_Marysvale"/> [[Basalt]]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 {{convert|900|ft|m|-2}} and are now in direct contact with the much older Claron Formation.<ref name="GUSP5th526">Kiver and Harris (1999). ''Geology of U.S. Parklands'', page 526</ref> ==Late Cenozoic tectonics== ===Formation of the High Plateaus=== [[Image:Colorado Plateaus map2.jpg|frame|right|Colorado Plateaus map]] 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 50- to 100-foot-thick (15 to 30&nbsp;m) [[Oligocene]] or [[Miocene]]-aged [[Boat Mesa Conglomerate]] and the [[Pliocene]] to early [[Pleistocene]]-aged [[Sevier River Formation]].<ref name="GNP5th53">Harris, Ann (1997). ''Geology of National Parks'', page 53</ref> The Boat Mesa is made mostly of conglomerates with minor amounts of sandstone and some limestone from lakes, representing stream and overbank flood deposits.<ref name="GBCNP46"/> The brownish-gray sandstone and gravels of the Sevier River Formation were laid down in valleys that were part of the ancestral [[Sevier River]] drainage system.<ref name="GNP5th53"/><ref name="GBCNP46"/> Around 15&nbsp;mya in [[Miocene]] time, tensional forces in [[Nevada]] to the west were so great that the crust was spread thin, creating the [[Basin and Range Province]].<ref name="GBCNP55"/> These same forces segmented what is now the western part of the [[Colorado Plateau]] into nine different smaller plateaus, including the [[Paunsaugunt Plateau|Paunsaugunt]] that the park sits astride.<ref name="GNP5th54">Harris, Ann (1997). ''Geology of National Parks'', page 54</ref><ref name="GUSP5th524">Kiver and Harris (1999). ''Geology of U.S. Parklands'', page 524</ref> Long, north–south-trending normal [[fault (geology)|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.<ref name="GBCNP55"/> 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&nbsp;feet (600&nbsp;m) relative to the Paria and Sevier valleys.<ref name="GUSP5th524"/> The [[Hurricane Fault]] marks the west edge of the [[Markagunt Plateau]] and is the topographic boundary between the Basin and Range and the Colorado Plateaus provinces.<ref name="GUSP5th524"/> [[Cedar Breaks National Monument]], 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]] to several thousand feet (over a kilometer) in elevation.<ref name="GNP5th53"/> 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.<ref name="GBCNP46"/> Whatever the order of events were, the High Plateaus region of the Colorado Plateau were by now nearly complete. ===Modern drainage and erosion=== {{seealso|Geology of the Grand Canyon area|Geology of the Canyonlands area}} Drainage of the Colorado Plateau was significantly altered by the opening of the [[Gulf of California]]. [[Rift]]ing tore [[Baja California Peninsula]] northwestward from the [[Mexico|Mexican]] mainland starting some 10 to 5&nbsp;mya.<ref name="GBCNP55"/> The ancestral [[Colorado River]] 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.<ref>Kiver and Harris (1999). ''Geology of U.S. Parklands'', page 407</ref> [[Headward erosion]] of one of those tributaries, the [[Paria River]], eroded north-northwestward toward what is now Paria Amphitheater.<ref name="GBCNP56">Davis and Pollock (2003). ''Geology of Bryce Canyon National Park'', page 56</ref> 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 [[hoodoo (geology)|hoodoos]]. Streams on the plateau do not contribute to the formation of alcoves or amphitheaters because they flow away from the rim.<ref name="GBCNP56"/> Erosion continues in this fashion today. ==Hoodoo formation in Bryce Canyon== [[Image:hoodoo formation-Big.jpg|right|Hoodoo formation]] The Pink Member of the Claron Formation is largely composed of easily eroded and relatively soft limestone. When rain combines with [[carbon dioxide]] 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]] 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.<ref name="NPS_Hoodoo">{{cite web|url=http://www.nps.gov/brca/naturescience/hoodoos.htm|title=Hoodoos|publisher=National Park Service|accessdate=2007-07-24}} (adapted public domain text)</ref> 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]]-rich limestone called [[dolomite]].<ref name="NPS_Hoodoo"/> Dolomite, being fortified by the mineral [[magnesium]], 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&ndash;4&nbsp;feet (0.6&ndash;1.3&nbsp;m) every 100 years.<ref name="NPS_Hoodoo"/> 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]]. 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.<ref name="NPS_Hoodoo"/> {{clear}} ==Notes== {{reflist|colwidth=35em}} ==References== *{{cite web|url=http://gsa.confex.com/gsa/2002RM/finalprogram/abstract_33476.htm|title=Volcanic rocks and ore deposits of the Marysvale Volcanic Field, west-central Utah |last=Cunningham|first=Charles G.|accessdate=2007-08-12|date=2002|publisher=The Geological Society of America}} *{{cite book|title=Geology of Utah's Parks and Monuments|publisher=Bryce Canyon Natural History Association and Utah Geological Association|date=August 2003|editor=Paul B. Anderson (editor)|chapter=Geology of Bryce Canyon National Park|last=Davis|first=George H.|coauthors=Pollock, Gayle L.|isbn=1882054105}} *{{cite book | title = Geology of National Parks | edition = Fifth Edition | author = Harris, Ann G | coauthors = Tuttle, Esther | location = Iowa | publisher = Kendall Hunt Publishing Co | date = 1997 | isbn = ISBN 0-7872-5353-7}} *{{cite book | author = Kiver, Eugene P | coauthors = Harris, David V | year = 1999 | title = Geology of U.S. Parklands | edition = 5th ed | publisher = John Wiley & Sons, Inc | location = New York | chapter = Bryce Canyon National Park and Cedar Breaks National Monument (Utah)|pages = 522-30|isbn=0-471-33218-6}} *{{cite book|url=http://geo-nsdi.er.usgs.gov/metadata/map-i/2645/a/metadata.faq.html#what | title=Geologic Map of the Central Marysvale Volcanic Field, Southwestern Utah|publisher=United States Geological Survey|accessdate=2007-08-12|last=Rowley|first=Peter D.|coauthors=Cunningham, Charles G.; Steven, Thomas A.; Workman, Jeremiah B.; Anderson, John J.; and Theissen, Kevin M.|date=2002|work=U.S. Geological Survey Geologic Investigations Series I-2645-A|location=Denver, Colorado}} *{{cite web|url=http://www.nps.gov/brca/naturescience/hoodoos.htm|title=Hoodoos|publisher=National Park Service|accessdate=2007-07-24}} (adapted public domain text) *{{cite web | url = http://www2.nature.nps.gov/geology/parks/brca/ | title = Geology field notes: Bryce Canyon National Park, Utah | publisher = National Park Service | date = [[2005-01-04]] | accessdate = 2007-08-02}} ==Further reading== * {{cite book | author = DeCourten, Frank | date = 1994 | title = Shadows of Time; the Geology of Bryce Canyon National Park | publisher = Bryce Canyon Natural History Association}} *{{cite book | title = Secrets in The Grand Canyon, Zion and Bryce Canyon National Parks | edition = Third Edition | author = Tufts, Lorraine Salem | location = North Palm Beach, Florida | publisher = National Photographic Collections | date = 1998 | isbn = 0-9620255-3-4}} [[Category:Geology of Utah]] [[Category:Bryce Canyon]] [[Category:Regional geology of the United States|Bryce Canyon]] [[de:Geologie des Bryce-Canyons]]