Arches National Park
Arches National Park is a national park in eastern Utah, United States. The park is adjacent to the Colorado River, 4 miles north of Utah. More than 2,000 natural sandstone arches are located in the park, including the well-known Delicate Arch, as well as a variety of unique geological resources and formations; the park contains the highest density of natural arches in the world. The park consists of 76,679 acres of high desert located on the Colorado Plateau; the highest elevation in the park is 5,653 feet at Elephant Butte, the lowest elevation is 4,085 feet at the visitor center. The park receives an average of less than 10 inches of rain annually. Administered by the National Park Service, the area was named a national monument on April 12, 1929, was redesignated as a national park on November 12, 1971; the park received more than 1.6 million visitors in 2018. The national park lies above an underground evaporite layer or salt bed, the main cause of the formation of the arches, balanced rocks, sandstone fins, eroded monoliths in the area.
This salt bed is thousands of feet thick in places, was deposited in the Paradox Basin of the Colorado Plateau some 300 million years ago when a sea flowed into the region and evaporated. Over millions of years, the salt bed was covered with debris eroded from the Uncompahgre Uplift to the northeast. During the Early Jurassic, desert conditions prevailed in the region and the vast Navajo Sandstone was deposited. An additional sequence of stream-laid and windblown sediments, the Entrada Sandstone, was deposited on top of the Navajo. Over 5,000 feet of younger sediments were deposited and have been eroded away. Remnants of the cover exist in the area including exposures of the Cretaceous Mancos Shale; the arches of the area are developed within the Entrada formation. The weight of this cover caused the salt bed below it to liquefy and thrust up layers of rock into salt domes; the evaporites of the area formed more unusual linear regions of uplift. Faulting occurred and whole sections of rock subsided into the areas between the domes.
In some places, they turned on edge. The result of one such 2,500-foot displacement, the Moab Fault, is seen from the visitor center; as this subsurface movement of salt shaped the landscape, erosion removed the younger rock layers from the surface. Except for isolated remnants, the major formations visible in the park today are the salmon-colored Entrada Sandstone, in which most of the arches form, the buff-colored Navajo Sandstone; these are visible in layer-cake fashion throughout most of the park. Over time, water seeped into the surface cracks and folds of these layers. Ice formed in the fissures and putting pressure on surrounding rock, breaking off bits and pieces. Winds cleaned out the loose particles. A series of free-standing fins remained. Wind and water attacked these fins until, in some, the cementing material gave way and chunks of rock tumbled out. Many damaged fins collapsed. Others, with the right degree of hardness and balance, survived despite their missing sections; these became the famous arches.
Although the park's terrain may appear rugged and durable, it is fragile. More than 1 million visitors each year threaten the fragile high-desert ecosystem; the problem lies within the soil's crust, composed of cyanobacteria, algae and lichens that grow in the dusty parts of the park. Factors that make Arches National Park sensitive to visitor damage include being a semiarid region, the scarce, unpredictable rainfall, lack of deep freezing, lack of plant litter, which results in soils that have both a low resistance to, slow recovery from, compressional forces such as foot traffic. Methods of indicating effects on the soil are cytophobic soil crust index, measuring of water infiltration, t-tests that are used to compare the values from the undisturbed and disturbed areas. Humans have occupied the region since the last ice age 10,000 years ago. Fremont people and Ancient Pueblo People lived in the area until about 700 years ago. Spanish missionaries encountered Ute and Paiute tribes in the area when they first came through in 1775, but the first European-Americans to attempt settlement in the area were the Mormon Elk Mountain Mission in 1855, who soon abandoned the area.
Ranchers and prospectors settled Moab in the neighboring Riverine Valley in the 1880s. Word of the beauty of the surrounding rock formations spread beyond the settlement as a possible tourist destination; the Arches area was first brought to the attention of the National Park Service by Frank A. Wadleigh, passenger traffic manager of the Denver and Rio Grande Western Railroad. Wadleigh, accompanied by railroad photographer George L. Beam, visited the area in September 1923 at the invitation of Alexander Ringhoffer, a Hungarian-born prospector living in Salt Valley. Ringhoffer had written to the railroad in an effort to interest them in the tourist potential of a scenic area he had discovered the previous year with his two sons and a son-in-law, which he called the "Devil's Garden". Wadleigh was impressed by what Ringhoffer showed him, suggested to Park Service director Stephen T. Mather that the area be made a national monument; the following year, additional support for the monument idea came from Laurence Gould, a University of Michigan graduate student studying the geology of the nearby La Sal Mountains, shown the scenic area by local physician Dr. J. W. "Doc" Williams.
A succession of government investigators examined the area, in part due to confusion
National Park Service
The National Park Service is an agency of the United States federal government that manages all national parks, many national monuments, other conservation and historical properties with various title designations. It was created on August 25, 1916, by Congress through the National Park Service Organic Act and is an agency of the United States Department of the Interior; the NPS is charged with a dual role of preserving the ecological and historical integrity of the places entrusted to its management, while making them available and accessible for public use and enjoyment. As of 2018, the NPS employs 27,000 employees who oversee 419 units, of which 61 are designated national parks. National parks and national monuments in the United States were individually managed under the auspices of the Department of the Interior; the movement for an independent agency to oversee these federal lands was spearheaded by business magnate and conservationist Stephen Mather, as well as J. Horace McFarland. With the help of journalist Robert Sterling Yard, Mather ran a publicity campaign for the Department of the Interior.
They wrote numerous articles that praised the scenic and historic qualities of the parks and their possibilities for educational and recreational benefits. This campaign resulted in the creation of a National Park Service. On August 25, 1916, President Woodrow Wilson signed a bill that mandated the agency "to conserve the scenery and the natural and historic objects and wildlife therein, to provide for the enjoyment of the same in such manner and by such means as will leave them unimpaired for the enjoyment of future generations." Mather became the first director of the newly formed NPS. On March 3, 1933, President Herbert Hoover signed the Reorganization Act of 1933; the act would allow the President to reorganize the executive branch of the United States government. It wasn't until that summer when the new President, Franklin D. Roosevelt, made use of this power. Deputy Director Horace M. Albright had suggested to President Roosevelt that the historic sites from the American Civil War should be managed by the National Park Service, rather than the War Department.
President Roosevelt issued two Executive orders to make it happen. These two executive orders not only transferred to the National Park Service all the War Department historic sites, but the national monuments managed by the Department of Agriculture and the parks in and around the capital, run by an independent office. In 1951, Conrad Wirth became director of the National Park Service and went to work on bringing park facilities up to the standards that the public expected; the demand for parks after the end of the World War II had left the parks overburdened with demands that could not be met. In 1952, with the support of President Dwight D. Eisenhower, he began Mission 66, a ten-year effort to upgrade and expand park facilities for the 50th anniversary of the Park Service. New parks were added to preserve unique resources and existing park facilities were upgraded and expanded. In 1966, as the Park Service turned 50 years old, emphasis began to turn from just saving great and wonderful scenery and unique natural features to making parks accessible to the public.
Director George Hartzog began the process with the creation of the National Lakeshores and National Recreation Areas. Since its inception in 1916, the National Park Service has managed each of the United States' national parks, which have grown in number over the years to 60. Yellowstone National Park was the first national park in the United States. In 1872, there was no state government to manage it, so the federal government assumed direct control. Yosemite National Park began as a state park. Yosemite was returned to federal ownership. At first, each national park was managed independently, with varying degrees of success. In Yellowstone, the civilian staff was replaced by the U. S. Army in 1886. Due to the irregularities in managing these national treasures, Stephen Mather petitioned the federal government to improve the situation. In response, Secretary of the Interior Franklin K. Lane challenged him to lobby for creating a new agency, the National Park Service, to manage all national parks and some national monuments.
Mather was successful with the ratification of the National Park Service Organic Act in 1916. The agency was given authority over other protected areas, many with varying designations as Congress created them; the National Park System includes. The title or designation of a unit need not include the term park; the System as a whole is considered to be a national treasure of the United States, some of the more famous national parks and monuments are sometimes referred to metaphorically as "crown jewels". The system encompasses 84.4 million acres, of which more than 4.3 million acres remain in private ownership. The largest unit is Wrangell-St. Elias National Park and Preserve, Alaska. At 13,200,000 acres, it is over 16 percent of the entire system; the smallest unit in the system is Thaddeus Kosciuszko National Memorial, Pennsylvania, at 0.02 acre. In addition to administering its units and other properties, the National Park Service provides technical and financial assistance to several "affiliated areas" authorized by Congress.
The largest affiliated area is New Jersey Pinelands National Reserve at 1,164,025 acres. The smallest is Benjamin Franklin National Memorial at less than 0.01 acres. Although all units of the Nat
A fin is a geologic formation, a narrow, residual wall of hard sedimentary rock that remains standing after surrounding rock has been eroded away along parallel joints or fractures. Fins are formed when plateau develops many vertical, parallel cracks. There are two main modes of following erosion; the first is when water flows along joints and fractures and opens them wider and wider causing erosion. The second is where the rock type is harder and more erosion resistant than neighboring rocks, causing the weaker rock to fall away. Fins are considered an intermediary stage of many other erosional geologic features like windows and hoodoos; the formation of such features is a simplified four-step process. The first step is uplift that results in vertical fractures within the plateau; the second step is erosion that enlarges the fractures, producing fins. The third step is erosion attacking fins from below, causing arches; the fourth step is continuing weathering that enlarges holes, causing arches and holes to collapse, creating spires or hoodoos.
Fins will form in sedimentary rocks sandstone. Sandstone is bedded, which provides zones of weakness, along which weathering and erosion takes place. Iron oxide and calcium carbonate cemented sandstones produce fins; these are seen as weak cements, compared to the erosion resistant silica cement, but in arid and semi-arid regions they are much more resistant. This is due to the lack of water in these regions that would otherwise chemically weather iron oxide cements and calcium carbonate cements; because sandstones are bedded sedimentary rocks, they possess prominent joints and bedding planes which provides many channels for drainage. When drainage patterns follow these paths, it creates dendritic patterns within topography. Lack of soil cover in these dry regions gives joints maximum control over drainage systems resulting in angular patterns, striking topography, steep slopes. Fins occur in arid to semi-arid regions, like south western United States. Arches National Park in Utah is home to Navajo Sandstone, an iron oxide cement sandstone, displays all steps of the fin to spire erosion and formation process.
The Entrada Sandstone formation, a calcium carbonate cement sandstone, can be found within this region, along with Wyoming, New Mexico, Arizona
A canyon or gorge is a deep cleft between escarpments or cliffs resulting from weathering and the erosive activity of a river over geologic timescales. Rivers have a natural tendency to cut through underlying surfaces wearing away rock layers as sediments are removed downstream. A river bed will reach a baseline elevation, the same elevation as the body of water into which the river drains; the processes of weathering and erosion will form canyons when the river's headwaters and estuary are at different elevations through regions where softer rock layers are intermingled with harder layers more resistant to weathering. A canyon may refer to a rift between two mountain peaks, such as those in ranges including the Rocky Mountains, the Alps, the Himalayas or the Andes. A river or stream and erosion carve out such splits between mountains. Examples of mountain-type canyons are Provo Canyon in Utah or Yosemite Valley in California's Sierra Nevada. Canyons within mountains, or gorges that have an opening on only one side, are called box canyons.
Slot canyons are narrow canyons that have smooth walls. Steep-sided valleys in the seabed of the continental slope are referred to as submarine canyons. Unlike canyons on land, submarine canyons are thought to be formed by turbidity currents and landslides; the word canyon is Spanish in origin, with the same meaning. The word canyon is used in North America while the words gorge and ravine are used in Europe and Oceania, though gorge and ravine are used in some parts of North America. In the United States, place names use canyon in the southwest and gorge in the northeast, with the rest of the country graduating between these two according to geography. In Canada, a gorge is narrow while a ravine is more open and wooded; the military-derived word defile is used in the United Kingdom. Most canyons were formed by a process of long-time erosion from table-land level; the cliffs form because harder rock strata that are resistant to erosion and weathering remain exposed on the valley walls. Canyons are much more common in arid than in wet areas because physical weathering has a more localized effect in arid zones.
The wind and water from the river combine to erode and cut away less resistant materials such as shales. The freezing and expansion of water serves to help form canyons. Water seeps into cracks between the rocks and freezes, pushing the rocks apart and causing large chunks to break off the canyon walls, in a process known as frost wedging. Canyon walls are formed of resistant sandstones or granite. Sometimes large rivers run through canyons as the result of gradual geological uplift; these are called entrenched rivers, because they are unable to alter their course. In the United States, the Colorado River in the Southwest and the Snake River in the Northwest are two examples of tectonic uplift. Canyons form in areas of limestone rock; as limestone is soluble to a certain extent, cave systems form in the rock. When these collapse, a canyon is left, as in the Mendip Hills in Somerset and Yorkshire Dales in Yorkshire, England. A box canyon is a small canyon, shorter and narrower than a river canyon, with steep walls on three sides, allowing access and egress only through the mouth of the canyon.
Box canyons were used in the western United States as convenient corrals, with their entrances fenced. The definition of "largest canyon" is imprecise, because a canyon can be large by its depth, its length, or the total area of the canyon system; the inaccessibility of the major canyons in the Himalaya contributes to their not being regarded as candidates for the biggest canyon. The definition of "deepest canyon" is imprecise if one includes mountain canyons as well as canyons cut through flat plateaus; the Yarlung Tsangpo Grand Canyon, along the Yarlung Tsangpo River in Tibet, is regarded by some as the deepest canyon in the world at 5,500 m. It is longer than the Grand Canyon in the United States. Others consider the Kali Gandaki Gorge in midwest Nepal to be the deepest canyon, with a 6400 m difference between the level of the river and the peaks surrounding it. Vying for deepest canyon in the Americas are the Cotahuasi Canyon and Colca Canyon, in southern Peru. Both have been measured at over 3500 m deep.
The Grand Canyon of northern Arizona in the United States, with an average depth of 1,600 m and a volume of 4.17 trillion cubic metres, is one of the world's largest canyons. It was among the 28 finalists of the New7Wonders of Nature worldwide poll; the largest canyon in Africa is the Fish River Canyon in Namibia. In August 2013, the discovery of Greenland's Grand Canyon was reported, based on the analysis of data from Operation IceBridge, it is located under an ice sheet. At 750 kilometres long, it is believed to be the longest canyon in the world; the Capertee Valley in Australia is reported as being the second largest canyon in the world. Some canyons have notable cultural significance. Evidence of early humanoids has been discovered in Africa's Olduvai Gorge. In the southwestern United States, canyons are important archeologically because of the many cliff-dwellings built in such areas by the ancient Pueblo people who were their first inhabitants; the following list contains only the most notable canyons of the world, arranged by continent and country.
Fish River Canyon Blyde Riv
Sandstone is a clastic sedimentary rock composed of sand-sized mineral particles or rock fragments. Most sandstone is composed of quartz or feldspar because they are the most resistant minerals to weathering processes at the Earth's surface, as seen in Bowen's reaction series. Like uncemented sand, sandstone may be any color due to impurities within the minerals, but the most common colors are tan, yellow, grey, pink and black. Since sandstone beds form visible cliffs and other topographic features, certain colors of sandstone have been identified with certain regions. Rock formations that are composed of sandstone allow the percolation of water and other fluids and are porous enough to store large quantities, making them valuable aquifers and petroleum reservoirs. Fine-grained aquifers, such as sandstones, are better able to filter out pollutants from the surface than are rocks with cracks and crevices, such as limestone or other rocks fractured by seismic activity. Quartz-bearing sandstone can be changed into quartzite through metamorphism related to tectonic compression within orogenic belts.
Sandstones are clastic in origin. They are formed from cemented grains that may either be fragments of a pre-existing rock or be mono-minerallic crystals; the cements binding these grains together are calcite and silica. Grain sizes in sands are defined within the range of 0.0625 mm to 2 mm. Clays and sediments with smaller grain sizes not visible with the naked eye, including siltstones and shales, are called argillaceous sediments; the formation of sandstone involves two principal stages. First, a layer or layers of sand accumulates as the result of sedimentation, either from water or from air. Sedimentation occurs by the sand settling out from suspension. Once it has accumulated, the sand becomes sandstone when it is compacted by the pressure of overlying deposits and cemented by the precipitation of minerals within the pore spaces between sand grains; the most common cementing materials are silica and calcium carbonate, which are derived either from dissolution or from alteration of the sand after it was buried.
Colors will be tan or yellow. A predominant additional colourant in the southwestern United States is iron oxide, which imparts reddish tints ranging from pink to dark red, with additional manganese imparting a purplish hue. Red sandstones are seen in the Southwest and West of Britain, as well as central Europe and Mongolia; the regularity of the latter favours use as a source for masonry, either as a primary building material or as a facing stone, over other forms of construction. The environment where it is deposited is crucial in determining the characteristics of the resulting sandstone, which, in finer detail, include its grain size and composition and, in more general detail, include the rock geometry and sedimentary structures. Principal environments of deposition may be split between terrestrial and marine, as illustrated by the following broad groupings: Terrestrial environmentsRivers Alluvial fans Glacial outwash Lakes Deserts Marine environmentsDeltas Beach and shoreface sands Tidal flats Offshore bars and sand waves Storm deposits Turbidites Framework grains are sand-sized detrital fragments that make up the bulk of a sandstone.
These grains can be classified into several different categories based on their mineral composition: Quartz framework grains are the dominant minerals in most clastic sedimentary rocks. These physical properties allow the quartz grains to survive multiple recycling events, while allowing the grains to display some degree of rounding. Quartz grains evolve from plutonic rock, which are felsic in origin and from older sandstones that have been recycled. Feldspathic framework grains are the second most abundant mineral in sandstones. Feldspar can be divided into two smaller subdivisions: plagioclase feldspars; the different types of feldspar can be distinguished under a petrographic microscope. Below is a description of the different types of feldspar. Alkali feldspar is a group of minerals in which the chemical composition of the mineral can range from KAlSi3O8 to NaAlSi3O8, this represents a complete solid solution. Plagioclase feldspar is a complex group of solid solution minerals that range in composition from NaAlSi3O8 to CaAl2Si2O8.
Lithic framework grains are pieces of ancient source rock that have yet to weather away to individual mineral grains, called lithic fragments or clasts. Lithic fragments can be any fine-grained or coarse-grained igneous, metamorphic, or sedimentary rock, although the most common lithic fragments found in sedimentary rocks are clasts of volcanic rocks. Accessory minerals are all other mineral grains in a sandstone. Common accessory minerals include micas, olivine and corundum. Many of these accessory grains are more dense than the silicates that
Utah is a state in the western United States. It became the 45th state admitted to the U. S. on January 4, 1896. Utah is the 13th-largest by area, 31st-most-populous, 10th-least-densely populated of the 50 United States. Utah has a population of more than 3 million according to the Census estimate for July 1, 2016. Urban development is concentrated in two areas: the Wasatch Front in the north-central part of the state, which contains 2.5 million people. Utah is bordered by Colorado to the east, Wyoming to the northeast, Idaho to the north, Arizona to the south, Nevada to the west, it touches a corner of New Mexico in the southeast. 62% of Utahns are reported to be members of The Church of Jesus Christ of Latter-day Saints, making Utah the only state with a majority population belonging to a single church. This influences Utahn culture and daily life; the LDS Church's world headquarters is located in Salt Lake City. The state is a center of transportation, information technology and research, government services, a major tourist destination for outdoor recreation.
In 2013, the U. S. Census Bureau estimated. St. George was the fastest-growing metropolitan area in the United States from 2000 to 2005. Utah has the 14th highest median average income and the least income inequality of any U. S. state. A 2012 Gallup national survey found Utah overall to be the "best state to live in" based on 13 forward-looking measurements including various economic and health-related outlook metrics. A common folk etymology is that the name "Utah" is derived from the name of the Ute tribe, purported to mean "people of the mountains" in the Ute language. However, the word for people in Ute is'núuchiu' while the word for mountain is'káav', offering no linguistic connection to the words'Ute' or'Utah'. According to other sources "Utah" is derived from the Apache name "yuttahih" which means "One, Higher up" or "Those that are higher up". In the Spanish language it was said as "Yuta", subsequently the English-speaking people adapted the word "Utah". Thousands of years before the arrival of European explorers, the Ancestral Puebloans and the Fremont people lived in what is now known as Utah, some of which spoke languages of the Uto-Aztecan group.
Ancestral Pueblo peoples built their homes through excavations in mountains, the Fremont people built houses of straw before disappearing from the region around the 15th century. Another group of Native Americans, the Navajo, settled in the region around the 18th century. In the mid-18th century, other Uto-Aztecan tribes, including the Goshute, the Paiute, the Shoshone, the Ute people settled in the region; these five groups were present. The southern Utah region was explored by the Spanish in 1540, led by Francisco Vásquez de Coronado, while looking for the legendary Cíbola. A group led by two Catholic priests—sometimes called the Dominguez-Escalante Expedition—left Santa Fe in 1776, hoping to find a route to the coast of California; the expedition encountered the native residents. The Spanish made further explorations in the region, but were not interested in colonizing the area because of its desert nature. In 1821, the year Mexico achieved its independence from Spain, the region became known as part of its territory of Alta California.
European trappers and fur traders explored some areas of Utah in the early 19th century from Canada and the United States. The city of Provo, Utah was named for one, Étienne Provost, who visited the area in 1825; the city of Ogden, Utah was named after Peter Skene Ogden, a Canadian explorer who traded furs in the Weber Valley. In late 1824, Jim Bridger became the first known English-speaking person to sight the Great Salt Lake. Due to the high salinity of its waters, He thought. After the discovery of the lake, hundreds of American and Canadian traders and trappers established trading posts in the region. In the 1830s, thousands of migrants traveling from the Eastern United States to the American West began to make stops in the region of the Great Salt Lake known as Lake Youta. Following the death of Joseph Smith in 1844, Brigham Young, as president of the Quorum of the Twelve, became the effective leader of the LDS Church in Nauvoo, Illinois. To address the growing conflicts between his people and their neighbors, Young agreed with Illinois Governor Thomas Ford in October 1845 that the Mormons would leave by the following year.
Young and the first band of Mormon pioneers reached the Salt Lake Valley on July 24, 1847. Over the next 22 years, more than 70,000 pioneers settled in Utah. For the first few years, Brigham Young and the thousands of early settlers of Salt Lake City struggled to survive; the arid desert land was deemed by the Mormons as desirable as a place where they could practice their religion without harassment. The Mormon settlements provided pioneers for other settlements in the West. Salt Lake City became the hub of a "far-flung commonwealth" of Mormon settlements. With new church converts coming from the East and around the world, Church leaders assigned groups of church members as missionaries to establish other settlements throughout the West, they developed irrigation to support large pioneer populations along Utah's Wasatch front. Throughout the remainder of the 19th century, Mormon pioneers established hundreds of other settlements in Utah, Id
A natural arch, natural bridge, or rock arch is a natural rock formation where an arch has formed with an opening underneath. Natural arches form where inland cliffs, coastal cliffs, fins or stacks are subject to erosion from the sea, rivers or weathering. Most natural arches are formed from narrow fins and sea stacks composed of sandstone or limestone with steep vertical, cliff faces; the formations become narrower due to erosion over geologic time scales. The softer rock stratum erodes away creating rock shelters, or alcoves, on opposite sides of the formation beneath the harder stratum, or caprock, above it; the alcoves erode further into the formation meeting underneath the harder caprock layer, thus creating an arch. The erosional processes exploit weaknesses in the softer rock layers making cracks larger and removing material more than the caprock; the choice between bridge and arch is somewhat arbitrary. The Natural Arch and Bridge Society identifies a bridge as a subtype of arch, water-formed.
By contrast, the Dictionary of Geological Terms defines a natural bridge as a "natural arch that spans a valley of erosion."The largest natural arch, by a significant margin, is the Xianren Bridge in China, with a span of 122 ± 5 meters. On coasts two different types of arches can form depending on the geology. On discordant coastlines rock types run at 90° to the coast. Wave refraction concentrates the wave energy on the headland, an arch forms when caves break through the headland. Two examples of this type of arch are London Arch—previously known as London Bridge—in Victoria and Neill Island in the Andaman Islands, India; when these arches collapse, they form stacks and stumps. On concordant coastlines rock types run parallel to the coastline, with weak rock such as shale protected by stronger rock such as limestone; the wave action along concordant coastlines breaks through the strong rock and erodes the weak rock quickly. Good examples of this type of arch are the Durdle Door and Stair Hole near Lulworth Cove on Dorset's Jurassic Coast in south England.
When Stair Hole collapses it will form a cove. Weather-eroded arches begin their formation as deep cracks. Erosion occurring within the cracks wears away exposed rock layers and enlarges the surface cracks isolating narrow sandstone walls which are called fins. Alternating frosts and thawing cause crumbling and flaking of the porous sandstone and cut through some of the fins; the resulting holes become weathering. The arches collapse leaving only buttresses that in time will erode. Many weather-eroded arches are found in Arches National Park, Canyonlands National Park, Grand Staircase-Escalante National Monument, all located in southern Utah, United States; some natural bridges may look like arches, but they form in the path of streams that wear away and penetrate the rock. Pothole arches form by chemical weathering as water collects in natural depressions and cuts through to the layer below. Natural Bridges National Monument in Utah protects the area surrounding three large natural bridges, all of which were formed by streams running through canyons, the largest of, named Sipapu Bridge with a span of 225 feet.
The Rainbow Bridge National Monument's namesake was formed by flowing water which created the largest known natural bridge in the Western Hemisphere with a span of 234 feet, based on a laser measurement made in 2007. Xianren Bridge known as Fairy Bridge, in Guangxi, China is the world's largest known natural bridge with a span recorded at 400 feet by the Natural Arch and Bridge Society in October 2010, with a precision of ±15 feet. Natural bridges can form from natural limestone caves, where paired sinkholes collapse and a ridge of stone is left standing in between, with the cave passageway connecting from sinkhole to sinkhole. Like all rock formations, natural bridges are subject to continued erosion, will collapse and disappear. One example of this was the double-arched Victorian coastal rock formation, London Bridge, which lost an arch after storms increased erosion. Moon Hill in Yangshuo, Guizhou Province, China, is an example of an arch formed by the remnant of a karst limestone cave. In a few places in the world, natural arches are utilized by humans as transportation bridges with highways or railroads running across them.
In Virginia, US Route 11 traverses Natural Bridge. Two additional natural arch roadways are found in Kentucky; the first arch, a cave erosion arch made of limestone, is located in Carter Caves State Resort Park and it has a paved road on top. The second arch, a weather-eroded sandstone arch with a dirt road on top, is located on the edge of Natural Bridge State Park in Kentucky; the latter arch is called White's Branch Arch and the road going over it is referred to as the Narrows Road. In Europe, the Romanian village of Ponoarele has a road 60 m long and 13 m wide, passing over a stone arch 4 m thick, 20 m high, with a 9 m span; the arch is called God's Bridge. In South America, the railroad from Lima, Peru crosses the Rio Yauli on a natural bridge near kilometer 214.2 as it approaches the city of La Oroya, Peru. Aloba Arch, Chad Boatswain Bird Island, Ascension Island Bogenfels, Namibia Goedehoop natural rock bridge, South Africa Hole-in-the-Wall, Eastern Cape, South Africa Tassili n'Ajjer and Tadrart Rouge, two mountain ranges with many arches, Algeria Tukuyu natural bridge, Ta