TheColorado Plateau is aphysiographic anddesert region of theIntermontane Plateaus, roughly centered on theFour Corners region of theSouthwestern United States. This plateau covers an area of 130,000 sq mi (340,000 km2) within westernColorado, northwesternNew Mexico, southern and easternUtah, northernArizona, and a tiny fraction in the extreme southeast ofNevada. About 90% of the area is drained by theColorado River and its maintributaries: theGreen,San Juan, andLittle Colorado. Most of the remainder of the plateau is drained by theRio Grande and its tributaries.[1][2]: 395
The Colorado Plateau is largely made up of high desert, with scattered areas of forests. In the south-west corner of the Colorado Plateau, nicknamedHigh Country,[3] lies theGrand Canyon of the Colorado River. Much of the Plateau's landscape is related to the Grand Canyon in both appearance and geologic history. The nickname "Red Rock Country" suggests the brightly colored rock left bare to the view by dryness and erosion.Domes,hoodoos,fins,reefs, rivernarrows,natural bridges, andslot canyons are only some of the additional features typical of the Plateau.
The Colorado Plateau has the greatest concentration of U.S.National Park Service (NPS) units in thecountry outside the Washington, DC metropolitan area. Among its ninenational parks areGrand Canyon,Zion,Bryce Canyon,Capitol Reef,Canyonlands,Arches,Black Canyon,Mesa Verde, andPetrified Forest. Among its 18national monuments and other protected areas managed by the NPS, theUnited States Forest Service, and theBureau of Land Management areBears Ears,Rainbow Bridge,Dinosaur,Hovenweep,Wupatki,Sunset Crater Volcano,Grand Staircase–Escalante,Vermillion Cliffs,El Malpais,Natural Bridges,Canyons of the Ancients,Chaco Culture National Historical Park and theColorado National Monument.
This province is bounded by theRocky Mountains in Colorado and by theUinta Mountains andWasatch Mountains branches of the Rockies in northern and central Utah. It is also bounded by theRio Grande rift,Mogollon Rim, and theBasin and Range Province (at theHurricane Fault). Isolated ranges of theSouthern Rocky Mountains, such as theSan Juan Mountains in Colorado and theLa Sal Mountains in Utah, intermix into the central and southern parts of the Colorado Plateau.It is composed of six sections:[2]: 367
As the name implies, the High Plateaus Section is, on average, the highest section. North-south trendingnormal faults that include theHurricane, Sevier,Grand Wash, and Paunsaugunt separate the section's component plateaus.[2]: 366 This fault pattern is caused by the tensional forces pulling apart the adjacent Basin and Range Province to the west, making this section transitional. Occupying the southeast corner of the Colorado Plateau is the Datil Section. Thick sequences of mid-Tertiary to late-Cenozoic-agedlava covers this section. The development of the province has, in large part, been influenced by structural features in its oldest rocks. Part of theWasatch Line and its various faults form the province's western edge. Faults that run parallel to the Wasatch Fault that lies along theWasatch Range form the boundaries between the plateaus in the High Plateaus Section.[2]: 376 The Uinta Basin, Uncompahgre Uplift, and theParadox Basin were also formed by movement along structural weaknesses in the region's oldest rock.
In Utah, the province includes several higherfault-separatedplateaus:
Some sources also include the Tushar Mountain Plateau as part of the Colorado Plateau, but others do not. The mostly flat-lyingsedimentary rock units that make up these plateaus are found in component plateaus that are between 4,900 to 11,000 feet (1,500 to 3,350 m) above sea level. A supersequence of these rocks is exposed in the various cliffs and canyons (including theGrand Canyon) that make up theGrand Staircase. Increasingly younger east–west trending escarpments of the Grand Staircase extend north of the Grand Canyon and are named for their color:
Within these rocks are abundant mineral resources, including uranium, coal, petroleum, and natural gas. A study of the area's unusually clear geologic history (laid bare due to the arid and semiarid conditions) has greatly advanced that science. Arain shadow from theSierra Nevada far to the west and the many ranges of the Basin and Range means that the Colorado Plateau receives six to sixteen inches (15 to 40 cm) of annual precipitation.[2]: 369 Higher areas receive more precipitation and are covered in forests of pine, fir, and spruce. Though it can be said that the Plateau roughly centers on the Four Corners,Black Mesa in northern Arizona is much closer to the east–west, north–south midpoint of the Plateau Province. Lying southeast of Glen Canyon and southwest of Monument Valley at the north end of the Hopi Reservation, this remote coal-laden highland has about half of the Colorado Plateau's acreage north of it, half south of it, half west of it, and half east of it.
TheAmerican Association of Petroleum Geologists divides the Colorado Plateau into four geologic provinces. These are:[4]
TheAncestral Puebloan People lived in the region from roughly 2000 to 700 years ago.[2]: 374 A party from Santa Fe led byFathers Dominguez and Escalante, unsuccessfully seeking an overland route to California, made a five-month out-and-back trip through much of the Plateau in 1776–1777.[5] Despite having lost one arm in theAmerican Civil War,U.S. Army Major andgeologistJohn Wesley Powell explored the area in 1869 and 1872. Using wooden oak boats and small groups of men, thePowell Geographic Expedition charted this largely unknown region of the United States for the federal government.
Construction of theHoover Dam in the 1930s and theGlen Canyon Dam in the 1960s changed the character of the Colorado River. Dramatically reduced sediment load changed its color from reddish brown (Colorado isSpanish for "red-colored") to mostly clear. The apparent green color is fromalgae on the riverbed's rocks, not from any significant amount of suspended material. The lack of sediment has also starvedsand bars and beaches, but an experimental 12-day-long controlled flood from Glen Canyon Dam in 1996 showed substantial restoration. Similar floods are planned for every 5 to 10 years.[2]: 375 [needs update]
One of the most geologically intriguing features of the Colorado Plateau is its remarkable stability. Relatively little rock deformation such asfaulting andfolding has affected this high, thick crustal block within the last 600 million years or so, although there are some newer features such as theWaterpocket Fold of Capitol Reef (estimated 50–70 million years old). In contrast, provinces that have suffered severe deformation surround the plateau. Mountain building thrust up theRocky Mountains to the north and east and tremendous, earth-stretching tension produced theBasin and Range Province to the west and south. Sub ranges of theSouthern Rocky Mountains are scattered throughout the Colorado Plateau.[6]
ThePrecambrian andPaleozoic history of the Colorado Plateau is best revealed near its southern end, where theGrand Canyon has exposed rocks with ages that span almost 2 billion years. The oldest rocks at river level are igneous and metamorphic and have been lumped together asVishnu Basement Rocks; the oldest ages recorded by these rocks fall from 1950 to 1680 million years. Anerosion surface on the Vishnu Basement Rocks is covered by sedimentary rocks and basalt flows, and these rocks formed in the interval from about 1250 to 750 million years ago: in turn, they were uplifted and split into a range offault-block mountains.[2]: 383 Erosion greatly reduced this mountain range before the encroachment of a seaway along the passive western edge of the continent in the early Paleozoic. At the canyon rim is the Kaibab Formation, limestone deposited in the late Paleozoic (Permian) about 270 million years ago.
A 12,000-to-15,000-foot-high (3,700 to 4,600 m) extension of theAncestral Rocky Mountains called the Uncompahgre Mountains were uplifted and the adjacent Paradox Basin subsided. Almost 4 mi. (6.4 km) of sediment from the mountains andevaporites from the sea were deposited (seegeology of the Canyonlands area for detail).[2]: 383 Most of theformations were deposited in warm shallow seas and near-shore environments (such as beaches and swamps) as the seashore repeatedly advanced and retreated over the edge of a proto-North America (for detail, seegeology of the Grand Canyon area). The province was probably on acontinental margin throughout the late Precambrian and most of thePaleozoic era. Igneous rocks injected millions of years later form a marbled network through parts of the Colorado Plateau's darker metamorphic basement. By 600 million years ago North America had been leveled off to a remarkably smooth surface.
Throughout the Paleozoic Era, tropical seas periodically inundated the Colorado Plateau region. Thick layers of limestone, sandstone, siltstone, and shale were laid down in the shallow marine waters. During times when the seas retreated, stream deposits and dune sands were deposited or older layers were removed by erosion. Over 300 million years passed as layer upon layer of sediment accumulated.
It was not until the upheavals that coincided with the formation of the supercontinentPangea began about 250 million years ago that deposits of marine sediment waned and terrestrial deposits dominate. In late Paleozoic and much of theMesozoic era the region was affected by a series oforogenies (mountain-building events) that deformed western North America and caused a great deal of uplift. Eruptions from volcanic mountain ranges to the west buried vast regions beneath ashy debris. Short-lived rivers, lakes, and inland seas left sedimentary records of their passage. Streams, ponds and lakes produced formations such as the Chinle, Moenave, and Kayenta in the Mesozoic era. Later a vast desert formed the Navajo and Temple Cap formations and dry near-shore environment formed the Carmel (seegeology of the Zion and Kolob canyons area for details).
The area was again covered by a warm shallow sea when theCretaceous Seaway opened in late Mesozoic time. The Dakota Sandstone and the Tropic Shale were deposited in the warm shallow waters of this advancing and retreating seaway. Several other formations were also produced but were mostlyeroded following two major periods of uplift.
TheLaramide orogeny closed the seaway and uplifted a large belt of crust from Montana to Mexico, with the Colorado Plateau region being the largest block.Thrust faults in Colorado are thought to have formed from a slight clockwise movement of the region, which acted as a rigid crustal block. The Colorado Plateau Province was uplifted largely as a single block, possibly due to its relative thickness. This relative thickness may be why compressional forces from the orogeny were mostly transmitted through the province instead of deforming it.[2]: 376 Pre-existing weaknesses in Precambrian rocks were exploited and reactivated by the compression. It was along these ancient faults and other deeply buried structures that much of the province's relatively small and gently inclined flexures (such asanticlines,synclines, andmonoclines) formed.[2]: 376 Some of the prominent isolated mountain ranges of the Plateau, such asUte Mountain and theCarrizo Mountains, both near theFour Corners, are cored by igneous rocks that were emplaced about 70 million years ago.
Minor uplift events continued through the start of theCenozoic era and were accompanied by somebasaltic lava eruptions and mild deformation. The colorfulClaron Formation that forms the delicatehoodoos of Bryce Amphitheater and Cedar Breaks was then laid down as sediments in cool streams and lakes (seegeology of the Bryce Canyon area for details). The flat-lyingChuska Sandstone was deposited about 34 million years ago; the sandstone is predominantly of eolian origin and locally more than 500 meters thick. The Chuska Sandstone caps theChuska Mountains, and it lies unconformably on Mesozoic rocks deformed during theLaramide orogeny.
Younger igneous rocks form spectacular topographic features. TheHenry Mountains,La Sal Range, andAbajo Mountains, ranges that dominate many views in southeastern Utah, are formed about igneous rocks that were intruded in the interval from 20 to 31 million years: some igneous intrusions in these mountains formlaccoliths, a form of intrusion recognized byGrove Karl Gilbert during his studies of theHenry Mountains. Ship Rock (also calledShiprock), in northwestern New Mexico, and Church Rock andAgathla, nearMonument Valley, are erosional remnants of potassium-rich igneous rocks and associated breccias of the Navajo Volcanic Field, produced about 25 million years ago. TheHopi Buttes in northeastern Arizona are held up by resistant sheets of sodic volcanic rocks, extruded about 7 million years ago. More recent igneous rocks are concentrated nearer the margins of the Colorado Plateau. TheSan Francisco Peaks nearFlagstaff, south of theGrand Canyon, are volcanic landforms produced by igneous activity that began in that area about 6 million years ago and continued until 1064 CE, when basalt erupted inSunset Crater National Monument.Mount Taylor, nearGrants, New Mexico, is a volcanic structure with a history similar to that of the San Francisco Peaks: a basalt flow closer to Grants was extruded only about 3000 years ago (seeEl Malpais National Monument). These young igneous rocks may record processes in theEarth's mantle that are eating away at deep margins of the relatively stable block of the Plateau.
Tectonic activity resumed in Mid Cenozoic time and started to unevenly uplift and slightly tilt the Colorado Plateau region and the region to the west some 20 million years ago (as much as 3 kilometers of uplift occurred). Streams had theirgradient increased and they responded bydowncutting faster.Headward erosion andmass wasting helped to erode cliffs back into their fault-bounded plateaus, widening the basins in-between. Some plateaus have been so severely reduced in size this way that they becomemesas or evenbuttes. Monoclines form as a result of uplift bending the rock units. Eroded monoclines leave steeply tilted resistant rock called a hogback and the less steep version is a cuesta.
Great tension developed in the crust, probably related to changing plate motions far to the west. As the crust stretched, the Basin and Range Province broke up into a multitude of down-dropped valleys and elongate mountains. Major faults, such as the Hurricane Fault, developed that separate the two regions. The dry climate was in large part arainshadow effect resulting from the rise of theSierra Nevada further west. Yet for some reason not fully understood, the neighboring Colorado Plateau was able to preserve its structural integrity and remained a single tectonic block.[6]
A second mystery was that while the lower layers of the Plateau appeared to be sinking, overall the Plateau was rising. The reason for this was discovered upon analyzing data from theUSARRAY project. It was found that theasthenosphere had invaded the overlyinglithosphere, as a result of an area of mantle upwelling stemming from either the disintegration of the descendingFarallon Plate, or the survival of the subducted spreading center connected to theEast Pacific Rise andGorda Ridge beneath western North America, or possibly both. The asthenosphere erodes the lower levels of the Plateau. At the same time, as it cools, it expands and lifts the upper layers of the Plateau.[7][8] Eventually, the great block of Colorado Plateau crust rose a kilometer higher than the Basin and Range. As the land rose, the streams responded by cutting ever deeper stream channels. The most well-known of these streams, theColorado River, began to carve theGrand Canyon less than 6 million years ago.[6]
ThePleistocene epoch brought periodicice ages and a cooler, wetter climate. This increased erosion at higher elevations with the introduction ofalpine glaciers while mid-elevations were attacked byfrost wedging and lower areas by more vigorous stream scouring.Pluvial lakes also formed during this time. Glaciers and pluvial lakes disappeared and the climate warmed and became drier with the start ofHolocene epoch.
The Colorado Plateau is covered with dry grasslands and shrublands, openpinyon-juniper woodland, and mountain woodlands and forests.[9]
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Electrical power generation is one of the major industries that takes place in the Colorado Plateau region. Most electrical generation comes fromcoal fired power plants. The rocks of the Colorado Plateau are a source of oil and a major source ofnatural gas. Major petroleum deposits are present in theSan Juan Basin of New Mexico and Colorado, the Uinta Basin of Utah, thePiceance Basin of Colorado, and theParadox Basin of Utah, Colorado, and Arizona. The Colorado Plateau holds major uranium deposits, and there was a uranium boom in the 1950s. TheAtlas Uranium Mill near Moab has left a problematic tailings pile for cleanup. As of 2019[update], 10 million tons of tailings had been relocated out of an estimated 16 million tons.[10] Major coal deposits are being mined in the Colorado Plateau in Utah, Arizona, Colorado, and New Mexico, though large coal mining projects, such as on theKaiparowits Plateau, have been proposed and defeated politically. The ITT Power Project, eventually located inLynndyl, Utah, near Delta, was originally suggested for Salt Wash near Capitol Reef National Park. After a firestorm of opposition, it was moved to a less controversial site.[11] In Utah the largest deposits are in aptly named Carbon County. In Arizona the biggest operation is onBlack Mesa, supplying coal to Navajo Power Plant. Perhaps the only one of its kind, agilsonite plant near Bonanza, southeast ofVernal, Utah, mines this unique, lustrous, brittle form of asphalt, for use in "varnishes, paints,...ink, waterproofing compounds, electrical insulation,...roofing materials."[12]
This relatively high, semi-arid to arid province produces many distinctive erosional features such as arches,arroyos, canyons, cliffs, fins,natural bridges, pinnacles,hoodoos, andmonoliths that, in various places and extents, have been protected. Also protected are areas of historic or cultural significance, such as thepueblos of theAncestral Puebloan culture. There are nineU.S. National Parks, a National Historical Park, nineteenU.S. national monuments and dozens ofwilderness areas in the province along with millions of acres inU.S. National Forests, many state parks, and other protected lands. In fact, this region has the highest concentration of parklands in North America.[2]: 365 Lake Powell, in foreground, is not a natural lake but a reservoir impounded byGlen Canyon Dam.
National parks (from south to north to south clockwise):
National monuments (alphabetical):
Wilderness areas (alphabetical):
Other notable protected areas include:Barringer Crater,Dead Horse Point State Park,Glen Canyon National Recreation Area,Goblin Valley State Park,Goosenecks State Park, theGrand Gulch Primitive Area,Kodachrome Basin State Park,Monument Valley, and theSan Rafael Swell. Sedona, Arizona and Oak Creek Canyon lie on the south-central border of the Plateau. Many but not all of the Sedona area's cliff formations are protected as wilderness (Red Rock State Park andCoconino National Forest). The area has the visual appeal of a national park, but with a small, rapidly growing town in the center.
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This article incorporatespublic domain material from"Colorado Plateau Province".Geologic Provinces of the United States.United States Geological Survey. Archived fromthe original on 2017-07-09. Retrieved2017-07-04.{{cite book}}: CS1 maint: publisher location (link)
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