Question: When did the body of water crossed by Mike O'Callaghan–Pat Tillman Memorial Bridge start to form the grand canyon?

full_context: Document 1: London Bridge (Lake Havasu City): London Bridge is a bridge in Lake Havasu City, Arizona. It was built in the 1830s and formerly spanned the River Thames in London, England. It was dismantled in 1967 and relocated to Arizona. The Arizona bridge is a reinforced concrete structure clad in the original masonry of the 1830s bridge, which was purchased by Robert P. McCulloch from the City of London. McCulloch had exterior granite blocks from the original bridge numbered and transported to America to construct the present bridge in Lake Havasu City, a planned community he established in 1964 on the shore of Lake Havasu. The bridge was completed in 1971 (along with a canal), and links an island in the Colorado River with the main part of Lake Havasu City.
Document 2: Candor Chasma: Candor Chasma is one of the largest canyons in the Valles Marineris canyon system on Mars. The feature is geographically divided into two halves: East and West Candor Chasmas, respectively. It is unclear how the canyon originally formed; one theory is that it was expanded and deepened by tectonic processes similar to a graben, while another suggests that it was formed by subsurface water erosion similar to a karst. MRO discovered sulfates, hydrated sulfates, and iron oxides in Candor Chasma.
Document 3: Veterans Memorial Bridge (Bristol County, Massachusetts): The Veterans Memorial Bridge is a bascule bridge connecting Somerset, Massachusetts and Fall River, Massachusetts. The bridge carries U.S. Route 6 and Route 138 over the Taunton River, with connecting ramps to Route 79, and includes a bike path on its north side. The $290 million bridge was dedicated to area veterans on September 11, 2011. The bike path was also dedicated in a separate ceremony that same day in honor of Pvt. Michael E. Bouthot, who was killed in action in Iraq in 2006.
Document 4: Hoover Dam: 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, and cost over one hundred lives. Originally known as Boulder Dam from 1933, it was officially renamed Hoover Dam, for President Herbert Hoover, by a joint resolution of Congress in 1947.
Document 5: Grand Canyon: The Grand Canyon is a river valley in the Colorado Plateau that exposes uplifted Proterozoic and Paleozoic strata, and is also one of the six distinct physiographic sections of the Colorado Plateau province. It is not the deepest canyon in the world (Kali Gandaki Gorge in Nepal is much deeper). 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.
Document 6: Old Trails Bridge: The Old Trails Bridge over the Colorado River, brought a now-abandoned portion of U.S. Route 66 across from Needles, California to Topock, Arizona. It is a brace-ribbed through arch bridge that was built in 1915-1916. It served as a highway bridge until 1947 when the Red Rock Bridge, formerly a railroad bridge, was modified for highway use. The Old Trails Bridge was later converted to a pipeline bridge.
Document 7: Tonto Natural Bridge: Tonto Natural Bridge is a natural arch in Arizona, United States, that is believed to be the largest natural travertine bridge in the world. The area surrounding the bridge has been made into a state park called Tonto Natural Bridge State Park, which is located off State Route 87, just north of Payson. Tonto Natural Bridge stands over a tunnel that measures at its widest point and reaches a height of .
Document 8: Geology: All of these processes do not necessarily occur in a single environment, and do not necessarily occur in a single order. The Hawaiian Islands, for example, consist almost entirely of layered basaltic lava flows. The sedimentary sequences of the mid-continental United States and the Grand Canyon in the southwestern United States contain almost-undeformed stacks of sedimentary rocks that have remained in place since Cambrian time. Other areas are much more geologically complex. In the southwestern United States, sedimentary, volcanic, and intrusive rocks have been metamorphosed, faulted, foliated, and folded. Even older rocks, such as the Acasta gneiss of the Slave craton in northwestern Canada, the oldest known rock in the world have been metamorphosed to the point where their origin is undiscernable without laboratory analysis. In addition, these processes can occur in stages. In many places, the Grand Canyon in the southwestern United States being a very visible example, the lower rock units were metamorphosed and deformed, and then deformation ended and the upper, undeformed units were deposited. Although any amount of rock emplacement and rock deformation can occur, and they can occur any number of times, these concepts provide a guide to understanding the geological history of an area.
Document 9: Mike O'Callaghan–Pat Tillman Memorial Bridge: The Mike O'Callaghan–Pat Tillman Memorial Bridge is an arch bridge in the United States that spans the Colorado River between the states of Arizona and Nevada. The bridge is located within the Lake Mead National Recreation Area approximately southeast of Las Vegas, and carries Interstate 11 and U.S. Route 93 over the Colorado River. Opened in 2010, it was the key component of the Hoover Dam Bypass project, which rerouted US 93 from its previous routing along the top of Hoover Dam and removed several hairpin turns and blind curves from the route. It is jointly named for Mike O'Callaghan, Governor of Nevada from 1971–1979, and Pat Tillman, an American football player who left his career with the Arizona Cardinals to enlist in the United States Army and was later killed in Afghanistan by friendly fire.
Document 10: Hoover Dam: 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. Originally known as Boulder Dam from 1933, it was officially renamed Hoover Dam by a joint resolution of Congress in 1947. Its construction was the result of a massive effort involving thousands of workers, and cost over one hundred lives. The dam was named after President Herbert Hoover.
Document 11: Outflow channels: Outflow channels are extremely long, wide swathes of scoured ground on Mars, commonly containing the streamlined remnants of pre-existing topography and other linear erosive features indicating sculpting by fluids moving downslope. Channels extend many hundreds of kilometers in length and are typically greater than one kilometer in width; the largest valley (Kasei Vallis) is around long, greater than wide and exceeds in depth cut into the surrounding plains. These features tend to appear fully sized at fractures in the Martian surface, either from chaos terrains or from canyon systems or other tectonically controlled, deep graben, though there are exceptions. Besides their exceptional size, the channels are also characterized by low sinuosities and high width:depth ratios compared both to other Martian valley features and to terrestrial river channels. Crater counts indicate that most of the channels were cut since the early Hesperian, though the age of the features is variable between different regions of Mars. Some outflow channels in the Amazonis and Elysium Planitiae regions have yielded ages of only tens of million years, extremely young by the standards of Martian topographic features.
Document 12: New River Gorge Bridge: The roadway of the New River Gorge Bridge is 876 feet (267 m) above the New River. The New River Gorge Bridge is one of the highest vehicular bridges in the world, and is currently the third highest in the United States. In 2005, the structure gained nationwide attention when the US Mint issued the West Virginia state quarter with the bridge depicted on one side. In 2013, the bridge was listed on the National Register of Historic Places.
Document 13: Geological history of Earth: The geological history of Earth follows the major events in Earth's past based on the geologic time scale, a system of chronological measurement based on the study of the planet's rock layers (stratigraphy). Earth formed about 4.54 billion years ago by accretion from the solar nebula, a disk - shaped mass of dust and gas left over from the formation of the Sun, which also created the rest of the Solar System.
Document 14: Grand Canyon: 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, simultaneously deepening and widening the canyon.
Document 15: Grand Canyon: The Grand Canyon (Hopi: Ongtupqa; Yavapai: Wi: kaʼi: la, Navajo: Tsékooh Hatsoh, Spanish: Gran Cañón) is a steep - sided canyon carved by the Colorado River in Arizona, United States. The Grand Canyon is 277 miles (446 km) long, up to 18 miles (29 km) wide and attains a depth of over a mile (6,093 feet or 1,857 meters).
ground_truth: about 5 to 6 million years ago
sub_queries: Mike O'Callaghan–Pat Tillman Memorial Bridge >> crosses Answer: Colorado River
when did Colorado River start to form the grand canyon Answer: about 5 to 6 million years ago