Hoover Dam is a concrete arch-gravity dam in the Black Canyon of the Colorado River, on the border between the U. S. states of Nevada and Arizona. It was constructed between 1931 and 1936 during the Great Depression and was dedicated on September 30, 1935, by President Franklin D. Roosevelt, its construction was the result of a massive effort involving thousands of workers, cost over one hundred lives. Known as Boulder Dam from 1933, it was renamed Hoover Dam, for President Herbert Hoover, by a joint resolution of Congress in 1947. Since about 1900, the Black Canyon and nearby Boulder Canyon had been investigated for their potential to support a dam that would control floods, provide irrigation water and produce hydroelectric power. In 1928, Congress authorized the project; the winning bid to build the dam was submitted by a consortium called Six Companies, Inc. which began construction on the dam in early 1931. Such a large concrete structure had never been built before, some of the techniques were unproven.
The torrid summer weather and lack of facilities near the site presented difficulties. Six Companies turned the dam over to the federal government on March 1, 1936, more than two years ahead of schedule. Hoover Dam impounds the largest reservoir in the United States by volume; the dam is located near Boulder City, Nevada, a municipality constructed for workers on the construction project, about 30 mi southeast of Las Vegas, Nevada. The dam's generators provide power for public and private utilities in Nevada and California. Hoover Dam is a major tourist attraction; the traveled U. S. Route 93 ran along the dam's crest until October 2010; as the United States developed the Southwest, the Colorado River was seen as a potential source of irrigation water. An initial attempt at diverting the river for irrigation purposes occurred in the late 1890s, when land speculator William Beatty built the Alamo Canal just north of the Mexican border. Though water from the Imperial Canal allowed for the widespread settlement of the valley, the canal proved expensive to maintain.
After a catastrophic breach that caused the Colorado River to fill the Salton Sea, the Southern Pacific Railroad spent $3 million in 1906–07 to stabilize the waterway, an amount it hoped in vain would be reimbursed by the Federal Government. After the waterway was stabilized, it proved unsatisfactory because of constant disputes with landowners on the Mexican side of the border; as the technology of electric power transmission improved, the Lower Colorado was considered for its hydroelectric-power potential. In 1902, the Edison Electric Company of Los Angeles surveyed the river in the hope of building a 40-foot rock dam which could generate 10,000 horsepower. However, at the time, the limit of transmission of electric power was 80 miles, there were few customers within that limit. Edison allowed land options it held on the river to lapse—including an option for what became the site of Hoover Dam. In the following years, the Bureau of Reclamation, known as the Reclamation Service at the time considered the Lower Colorado as the site for a dam.
Service chief Arthur Powell Davis proposed using dynamite to collapse the walls of Boulder Canyon, 20 miles north of the eventual dam site, into the river. The river would carry off the smaller pieces of debris, a dam would be built incorporating the remaining rubble. In 1922, after considering it for several years, the Reclamation Service rejected the proposal, citing doubts about the unproven technique and questions as to whether it would in fact save money. In 1922, the Reclamation Service presented a report calling for the development of a dam on the Colorado River for flood control and electric power generation; the report was principally authored by Davis, was called the Fall-Davis report after Interior Secretary Albert Fall. The Fall-Davis report cited use of the Colorado River as a federal concern because the river's basin covered several states, the river entered Mexico. Though the Fall-Davis report called for a dam "at or near Boulder Canyon", the Reclamation Service found that canyon unsuitable.
One potential site at Boulder Canyon was bisected by a geologic fault. The Service found it ideal. Despite the site change, the dam project was referred to as the "Boulder Canyon Project". With little guidance on water allocation from the Supreme Court, proponents of the dam feared endless litigation. A Colorado attorney proposed that the seven states which fell within the river's basin form an interstate compact, with the approval of Congress; such compacts were authorized by Article I of the United States Constitution but had never been concluded among more than two states. In 1922, representatives of seven states met with then-Secretary of Commerce Herbert Hoover. Initial talks produced no result, but when the Supreme Court handed down the Wyoming v. Colorado decision undermining the claims of the upstream states, they became anxious to reach an agreement; the resulting Colorado River Compact was signed on November 24, 1922. Legislation to authorize the dam was introduced by two California Republicans, Representative Phi
The Salton Sea is a shallow, endorheic rift lake located directly on the San Andreas Fault, predominantly in the U. S. state of California's Imperial and Coachella valleys. The lake occupies the lowest elevations of the Salton Sink in the Colorado Desert of Imperial and Riverside counties in Southern California, its surface is 236.0 ft below sea level as of January 2018. The deepest point of the sea is 5 ft higher than the lowest point of Death Valley; the sea is fed by the New and Alamo Rivers, as well as agricultural runoff, drainage systems, creeks. Over millions of years, the Colorado River has flowed into the Imperial Valley and deposited soil, building up the terrain and changing the course of the river. For thousands of years, the river has alternately flowed into and out of the valley, alternately creating a freshwater lake, an saline lake, a dry desert basin, depending on river flows and the balance between inflow and evaporative loss; the cycle of filling has repeated many times. The latest natural cycle occurred around 1600–1700 as remembered by Native Americans who talked with the first European settlers.
Fish traps still exist at many locations, the Native Americans evidently moved the traps depending upon the cycle. The most recent inflow of water from the now controlled Colorado River was accidentally created by the engineers of the California Development Company in 1905. In an effort to increase water flow into the area for farming, irrigation canals were dug from the Colorado River into the valley; the canals suffered silt buildup, so a cut was made in the bank of the Colorado River to further increase the water flow. The resulting outflow overwhelmed the engineered canal near Yuma and the river flowed into the Salton Basin for two years, filling the historic dry lake bed and creating the modern sea, before repairs were completed. While it varies in dimensions and area with fluctuations in agricultural runoff and rainfall, the Salton Sea is about 15 by 35 miles. With an estimated surface area of 343 square miles or 350 square miles, the Salton Sea is the largest lake in California; the average annual inflow is less than 1.2 million acre⋅ft, enough to maintain a maximum depth of 43 feet and a total volume of about 6 million acre⋅ft.
However, due to changes in water apportionments agreed upon for the Colorado River under the Quantification Settlement Agreement of 2003, the overall water level of the sea is expected to decrease between 2013 and 2021. The lake's salinity, about 56 grams per litre, is greater than that of the Pacific Ocean, but less than that of the Great Salt Lake; the concentration has been increasing at a rate of about 3% per year. About 4 million short tons of salt are deposited in the valley each year; the area was once part of a vast inland sea. Geologists estimate that for three million years, at least through all the years of the Pleistocene glacial age, a large delta was deposited by the Colorado River in the southern region of the Imperial Valley; the delta reached the western shore of the Gulf of California, creating a barrier that separated the area of the Salton Sea from the northern reaches of the Gulf. Were it not for this barrier, the entire Salton Sink along with the Imperial Valley would be submerged as the Gulf would extend as far north as Indio.
Since the exclusion of the ocean, the Salton Basin has over the ages been alternately a freshwater lake, an saline endorheic lake, a dry desert basin, depending on river flows and the balance between inflow and evaporative loss. A lake exists only during times it is replenished by the rivers and rainfall, a cycle that has repeated many times over hundreds of thousands of years cycling every 400 to 500 years. Evidence that the basin was occupied periodically by multiple lakes includes wave-cut shorelines at various elevations preserved on the hillsides of the east and west margins of the present lake, the Salton Sea; these indicate that the basin was occupied intermittently as as a few hundred years ago. The last of the Pleistocene lakes to occupy the basin was Lake Cahuilla periodically identified on older maps as Lake LeConte or the Blake Sea, after American professor and geologist William Phipps Blake. Throughout the Spanish period of California's history, the area was referred to as the "Colorado Desert" after the Colorado River.
In a railroad survey completed in 1855, it was called "the Valley of the Ancient Lake". On several old maps from the Library of Congress, it has been found labeled "Cahuilla Valley" and "Cabazon Valley". "Salt Creek" first appeared on a map in 1867 and "Salton Station" is on a railroad map from 1900, although this place had been there as a rail stop since the late 1870s. Until the advent of the modern sea, the Salton Sink was the site of a major salt-mining operation. In 1900, the California Development Company began construction of irrigation canals to divert water from the Colorado River into the Salton Sink, a dry lake bed. After construction of these irrigation canals, the Salton Sink became fertile for a time, allowing farmers to plant crops. Within two years, the Imperial Canal became filled with silt from the Colorado River. Engineers tried to alleviate the blockages to no avail. In 1905, heavy rainfall and snowmelt caused the Colorado River to swell, overrunning a set of headgates for the Alamo Canal.
Blythe is a city in Riverside County, United States, in the Palo Verde Valley of the Lower Colorado River Valley region, an agricultural area and part of the Colorado Desert along the Colorado River 224 miles east of Los Angeles and 150 miles west of Phoenix. Blythe was named after Thomas H. Blythe, a San Francisco financier, who established primary water rights to the Colorado River in the region in 1877; the city was incorporated on July 21, 1916. The population was 20,817 at the 2010 census. In the early or mid-1870s, William Calloway, an engineer and a former captain of the 1st California Infantry Regiment, explored an area across the Colorado River from Ehrenberg and found its potential for development. Calloway made preliminary surveys and filed land claims under the Swamp Land Act of 1850, he interested the wealthier Thomas Henry Blythe, born in Mold, Wales, to undertake development and settlement of an "empire" located next to the Colorado. On July 17, 1877, Blythe filed his first claim for Colorado River water on what was to become the "Blythe Intake".
Blythe appointed another man named George Irish as manager to assist Calloway in building an irrigation system. Calloway died in a Chemehuevi attack in March 28, 1880, was replaced by C. C. Miller, the father of Frank Augustus Miller. Thomas Blythe died on April 4, 1883. After his death, the work in the valley halted and Blythe's estate subsequently went into litigation between his illegitimate daughter Florence and other claimants, the trial beginning on 1889. By the 1900s, Florence was awarded the estate, after several years of preceding rulings in favor of her and appeals against her. Frank Murphy and Ed Williams, who were involved on the cattle industry in southeastern Arizona, came to the area in 1904 and were convinced it was well-suited for cattle and farming. With the Hobson brothers from Ventura County, they bought Blythe's estate and formed the Palo Verde Land and Water Company. During 1911–1912, W. F. Holt, who helped develop nearby Imperial Valley, was the company's general manager. On August 8, 1916, the California Southern Railroad reached Blythe from the desert station of Rice known as Blythe Junction.
It was renamed to honor G. W. Rice, an engineer and superintendent of the railroad; the dramatic growth in the valley following this event attracted national attention. Production totals increased annually from nothing to near $8,000,000 in few years from cotton and cotton seed shipped to the ports; the lower cotton prices in 1920 ended this prosperous time. The Atchison and Santa Fe Railway began leasing the line in 1921 and acquired it in the end of 1942. In 1935, the completion of Boulder Dam extinguished the destructive annual floods in the valley; as noted in the city's fiftieth anniversary, some forty crops were grown in the farms, large cattle feeds were another aspect of the agriculture industry. Nearly two decades earlier, the Fisher ranch had the biggest herd of registered Brahman cattle in California, the breeding stock having been sold to western states and other countries. During World War II, Blythe was the site of United States Army Air Forces facilities in the Blythe Airport and the Gary Field.
The first automobile bridge over the Colorado River between Blythe and Ehrenberg was constructed in 1928 to replace a cable ferry service. The bridge's successor was built in the early 1960s and it was expanded to four lanes and a pedestrian walkway in early 1974. In 1972, Interstate 10 was built through the city, replacing US 60 and the decommissioned US 70 in Hobsonway as the main thoroughfare. In 2016, the voter-approved recreational use of cannabis in California has made the cannabis industry drawn to the economically declined city due to lower land prices and lower taxes compared to other parts of the state. One of the proposed cannabis facilities, Palo Verde Center, would be one of the largest in North America. Blythe is located near the California/Arizona border in the Colorado Desert section of the Sonoran Desert, at the junction of Interstate 10 and US 95. According to the United States Census Bureau, the city has a total area of 27.0 square miles, of which 26.2 square miles is land and 0.8 square miles is water.
Nearby communities include Lost Lake and Vidal to the north, Ripley to the south, Desert Center to the west, Ehrenberg, Arizona, to the east. Major cities in the region include Yuma, Phoenix, San Bernardino and Las Vegas. Blythe is within 4 hours via car of 10% of the United States' population. Blythe has a hot desert climate, featuring hot summers and mild winters. There are an average of 178.4 days with highs of higher. There are an average of 18.9 days with lows of 32 °F or lower. Until 2016, the record high temperature was 122 °F on July 7, 1920, June 24, 1929, but on June 20, 2016, that long-standing record was shattered when Blythe reached 124 °F. The record low temperature was 5 °F on January 6, 1913. There are an average of 16 days with measurable precipitation; the wettest year was 1951 with 8.71 inches and the driest year was 1956 with.18 inches. The most rainfall in one month was 6.00 inches in August 1951, which included the 24-hour record rainfall of 3.06 inches on August 27. At the airport, there are an average of 176.0 days with highs of higher.
There are an average of 5.4 days with lows of lower. The record high temperature was 124 °F on June 20, 2016; the recor
Wyoming is a state in the mountain region of the western United States. The state is the 10th largest by area, the least populous, the second most sparsely populated state in the country. Wyoming is bordered on the north by Montana, on the east by South Dakota and Nebraska, on the south by Colorado, on the southwest by Utah, on the west by Idaho and Montana; the state population was estimated at 577,737 in 2018, less than 31 of the most populous U. S. cities including Denver in neighboring Colorado. Cheyenne is the state capital and the most populous city, with an estimated population of 63,624 in 2017; the western two-thirds of the state is covered by the mountain ranges and rangelands of the Rocky Mountains, while the eastern third of the state is high elevation prairie called the High Plains. Half of the land in Wyoming is owned by the U. S. government, leading Wyoming to rank sixth by area and fifth by proportion of a state's land owned by the federal government. Federal lands include two national parks—Grand Teton and Yellowstone—two national recreation areas, two national monuments, several national forests, historic sites, fish hatcheries, wildlife refuges.
Original inhabitants of the region include the Crow, Arapaho and Shoshone. Southwestern Wyoming was in the Spanish Empire and Mexican territory until it was ceded to the United States in 1848 at the end of the Mexican–American War; the region acquired the name Wyoming when a bill was introduced to the U. S. Congress in 1865 to provide a "temporary government for the territory of Wyoming"; the name was used earlier for the Wyoming Valley in Pennsylvania, is derived from the Munsee word xwé:wamənk, meaning "at the big river flat". The main drivers of Wyoming's economy are mineral extraction—mostly coal, natural gas, trona—and tourism. Agricultural commodities include livestock, sugar beets and wool; the climate is semi-arid and continental and windier than the rest of the U. S. with greater temperature extremes. Wyoming has been a politically conservative state since the 1950s, with the Republican Party candidate winning every presidential election except 1964. Wyoming's climate is semi-arid and continental, is drier and windier in comparison to most of the United States with greater temperature extremes.
Much of this is due to the topography of the state. Summers in Wyoming are warm with July high temperatures averaging between 85 and 95 °F in most of the state. With increasing elevation, this average drops with locations above 9,000 feet averaging around 70 °F. Summer nights throughout the state are characterized by a rapid cooldown with the hottest locations averaging in the 50–60 °F range at night. In most of the state, most of the precipitation tends to fall in early summer. Winters are cold, but are variable with periods of sometimes extreme cold interspersed between mild periods, with Chinook winds providing unusually warm temperatures in some locations. Wyoming is a dry state with much of the land receiving less than 10 inches of rainfall per year. Precipitation depends on elevation with lower areas in the Big Horn Basin averaging 5–8 inches; the lower areas in the North and on the eastern plains average around 10–12 inches, making the climate there semi-arid. Some mountain areas do receive a good amount of precipitation, 20 inches or more, much of it as snow, sometimes 200 inches or more annually.
The state's highest recorded temperature is 114 °F at Basin on July 12, 1900 and the lowest recorded temperature is −66 °F at Riverside on February 9, 1933. The number of thunderstorm days vary across the state with the southeastern plains of the state having the most days of thunderstorm activity. Thunderstorm activity in the state is highest during early summer; the southeastern corner of the state is the most vulnerable part of the state to tornado activity. Moving away from that point and westwards, the incidence of tornadoes drops with the west part of the state showing little vulnerability. Tornadoes, where they occur, tend to be small and brief, unlike some of those that occur farther east; as specified in the designating legislation for the Territory of Wyoming, Wyoming's borders are lines of latitude 41°N and 45°N, longitude 104°3'W and 111°3'W, making the shape of the state a latitude-longitude quadrangle. Wyoming is one of only three states to have borders along only straight latitudinal and longitudinal lines, rather than being defined by natural landmarks.
Due to surveying inaccuracies during the 19th century, Wyoming's legal border deviates from the true latitude and longitude lines by up to half of a mile in some spots in the mountainous region along the 45th parallel. Wyoming is bordered on the north by Montana, on the east by South Dakota and Nebraska, on the south by Colorado, on the southwest by Utah, on the west by Idaho, it is the tenth largest state in the United States in total area, containing 97,814 square miles and is made up of 23 counties. From the north border to the south border it is 276 miles; the Great Plains meet the Rocky Mountains in Wyoming. The state is a great plateau broken by many mountain ranges. Surface elevations range from the summit of Gannett Peak in the Wind River Mountain Range, at 13,804 feet, to the Belle Fourche River val
Colorado is a state of the Western United States encompassing most of the southern Rocky Mountains as well as the northeastern portion of the Colorado Plateau and the western edge of the Great Plains. It is the 8th most extensive and 21st most populous U. S. state. The estimated population of Colorado was 5,695,564 on July 1, 2018, an increase of 13.25% since the 2010 United States Census. The state was named for the Colorado River, which early Spanish explorers named the Río Colorado for the ruddy silt the river carried from the mountains; the Territory of Colorado was organized on February 28, 1861, on August 1, 1876, U. S. President Ulysses S. Grant signed Proclamation 230 admitting Colorado to the Union as the 38th state. Colorado is nicknamed the "Centennial State" because it became a state one century after the signing of the United States Declaration of Independence. Colorado is bordered by Wyoming to the north, Nebraska to the northeast, Kansas to the east, Oklahoma to the southeast, New Mexico to the south, Utah to the west, touches Arizona to the southwest at the Four Corners.
Colorado is noted for its vivid landscape of mountains, high plains, canyons, plateaus and desert lands. Colorado is part of the western and southwestern United States, is one of the Mountain States. Denver is most populous city of Colorado. Residents of the state are known as Coloradans, although the antiquated term "Coloradoan" is used. Colorado is notable for its diverse geography, which includes alpine mountains, high plains, deserts with huge sand dunes, deep canyons. In 1861, the United States Congress defined the boundaries of the new Territory of Colorado by lines of latitude and longitude, stretching from 37°N to 41°N latitude, from 102°02'48"W to 109°02'48"W longitude. After 158 years of government surveys, the borders of Colorado are now defined by 697 boundary markers and 697 straight boundary lines. Colorado and Utah are the only states that have their borders defined by straight boundary lines with no natural features; the southwest corner of Colorado is the Four Corners Monument at 36°59'56"N, 109°2'43"W.
This is the only place in the United States where four states meet: Colorado, New Mexico and Utah. The summit of Mount Elbert at 14,440 feet elevation in Lake County is the highest point in Colorado and the Rocky Mountains of North America. Colorado is the only U. S. state that lies above 1,000 meters elevation. The point where the Arikaree River flows out of Yuma County and into Cheyenne County, Kansas, is the lowest point in Colorado at 3,317 feet elevation; this point, which holds the distinction of being the highest low elevation point of any state, is higher than the high elevation points of 18 states and the District of Columbia. A little less than half of Colorado is flat and rolling land. East of the Rocky Mountains are the Colorado Eastern Plains of the High Plains, the section of the Great Plains within Nebraska at elevations ranging from 3,350 to 7,500 feet; the Colorado plains are prairies but include deciduous forests and canyons. Precipitation averages 15 to 25 inches annually. Eastern Colorado is presently farmland and rangeland, along with small farming villages and towns.
Corn, hay and oats are all typical crops. Most villages and towns in this region boast both a grain elevator. Irrigation water is available from subterranean sources. Surface water sources include the South Platte, the Arkansas River, a few other streams. Subterranean water is accessed through artesian wells. Heavy use of wells for irrigation caused underground water reserves to decline. Eastern Colorado hosts considerable livestock, such as hog farms. 70% of Colorado's population resides along the eastern edge of the Rocky Mountains in the Front Range Urban Corridor between Cheyenne and Pueblo, Colorado. This region is protected from prevailing storms that blow in from the Pacific Ocean region by the high Rockies in the middle of Colorado; the "Front Range" includes Denver, Fort Collins, Castle Rock, Colorado Springs, Pueblo and other townships and municipalities in between. On the other side of the Rockies, the significant population centers in Western Colorado are the cities of Grand Junction and Montrose.
The Continental Divide of the Americas extends along the crest of the Rocky Mountains. The area of Colorado to the west of the Continental Divide is called the Western Slope of Colorado. West of the Continental Divide, water flows to the southwest via the Colorado River and the Green River into the Gulf of California. Within the interior of the Rocky Mountains are several large parks which are high broad basins. In the north, on the east side of the Continental Divide is the North Park of Colorado; the North Park is drained by the North Platte River, which flows north into Nebraska. Just to the south of North Park, but on the western side of the Continental Divide, is the Middle Park of Colorado, drained by the Colorado River; the South Park of Colorado is the region of the headwaters of the South Platte River. In southmost Colorado is the large San Luis Valley, where the headwaters of the Rio Grande are located; the valley sits between the Sangre De Cristo Mountains and San Juan Mountains, consists of large desert lands that run into the mountains.
The Rio Grande drains due south into New Mexico and Texas. Across the Sangre de Cristo Range to the east of the S
The Grand Canyon is a steep-sided canyon carved by the Colorado River in Arizona, United States. The Grand Canyon is 277 miles long, up to 18 miles wide and attains a depth of over a mile; the canyon and adjacent rim are contained within Grand Canyon National Park, the Kaibab National Forest, Grand Canyon-Parashant National Monument, the Hualapai Indian Reservation, the Havasupai Indian Reservation and the Navajo Nation. President Theodore Roosevelt was a major proponent of preservation of the Grand Canyon area, visited it on numerous occasions to hunt and enjoy the scenery. Nearly two billion years of Earth's geological history have been exposed as the Colorado River and its tributaries cut their channels through layer after layer of rock while the Colorado Plateau was uplifted. While some aspects about the history of incision of the canyon are debated by geologists, several recent studies support the hypothesis that the Colorado River established its course through the area about 5 to 6 million years ago.
Since that time, the Colorado River has driven the down-cutting of the tributaries and retreat of the cliffs deepening and widening the canyon. For thousands of years, the area has been continuously inhabited by Native Americans, who built settlements within the canyon and its many caves; the Pueblo people considered the Grand Canyon a holy site, made pilgrimages to it. The first European known to have viewed the Grand Canyon was García López de Cárdenas from Spain, who arrived in 1540; the Grand Canyon is a river valley in the Colorado Plateau that exposes uplifted Proterozoic and Paleozoic strata, is one of the six distinct physiographic sections of the Colorado Plateau province. It is not the deepest canyon in the world. However, the Grand Canyon is known for its visually overwhelming size and its intricate and colorful landscape. Geologically, it is significant because of the thick sequence of ancient rocks that are well preserved and exposed in the walls of the canyon; these rock layers record much of the early geologic history of the North American continent.
Uplift associated with mountain formation moved these sediments thousands of feet upward and created the Colorado Plateau. The higher elevation has resulted in greater precipitation in the Colorado River drainage area, but not enough to change the Grand Canyon area from being semi-arid; the uplift of the Colorado Plateau is uneven, the Kaibab Plateau that Grand Canyon bisects is over one thousand feet higher at the North Rim than at the South Rim. All runoff from the North Rim flows toward the Grand Canyon, while much of the runoff on the plateau behind the South Rim flows away from the canyon; the result is deeper and longer tributary washes and canyons on the north side and shorter and steeper side canyons on the south side. Temperatures on the North Rim are lower than those on the South Rim because of the greater elevation. Heavy rains are common on both rims during the summer months. Access to the North Rim via the primary route leading to the canyon is limited during the winter season due to road closures.
The Grand Canyon is part of the Colorado River basin which has developed over the past 70 million years, in part based on apatite /He thermochronometry showing that Grand Canyon reached a depth near to the modern depth by 20 Ma. A recent study examining caves near Grand Canyon places their origins beginning about 17 million years ago. Previous estimates had placed the age of the canyon at 5–6 million years; the study, published in the journal Science in 2008, used uranium-lead dating to analyze calcite deposits found on the walls of nine caves throughout the canyon. There is a substantial amount of controversy because this research suggests such a substantial departure from prior supported scientific consensus. In December 2012, a study published in the journal Science claimed new tests had suggested the Grand Canyon could be as old as 70 million years. However, this study has been criticized by those who support the "young canyon" age of around six million years as " attempt to push the interpretation of their new data to their limits without consideration of the whole range of other geologic data sets."The canyon is the result of erosion which exposes one of the most complete geologic columns on the planet.
The major geologic exposures in the Grand Canyon range in age from the 2-billion-year-old Vishnu Schist at the bottom of the Inner Gorge to the 230-million-year-old Kaibab Limestone on the Rim. There is a gap of about a billion years between the 500-million-year-old stratum and the level below it, which dates to about 1.5 billion years ago. This large unconformity indicates a long period. Many of the formations were deposited in warm shallow seas, near-shore environments, swamps as the seashore advanced and retreated over the edge of a proto-North America. Major exceptions include the Permian Coconino Sandstone, which contains abundant geological evidence of aeolian sand dune deposition. Several parts of the Supai Group were deposited in non–marine environments; the great depth of the Grand Canyon and the height of its strata can be attributed to 5–10 thousand feet of uplift of the Colorado Plateau, starting about 65 million years ago. This uplift has steepened the stream gradient of the Colorado River