Question: When did the river crossed by the South Canon Bridge start to form the Grand Canyon?

full_context: Document 1: Glenwood Bridge: The Glenwood Bridge is a cantilever bridge in Pittsburgh, Pennsylvania, which carries Pennsylvania Route 885 over the Monongahela River. It started construction on June 3, 1958 and was completed in 1966 to replace an old decayed unsafe iron bridge built in 1894 which carried Pittsburgh Railways streetcar tracks and vehicle traffic on a wooden deck.
Document 2: 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 3: 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 4: Green Bay Road Bridge: The Green Bay Road Bridge is a Pratt pony truss bridge across the Manitowoc River in Manitowoc Rapids. The bridge was built in 1887 by the Wisconsin Bridge and Iron Company and was the second river crossing built at its location. Originally a road bridge, the bridge is now used for a bicycle and walking trail; it is in good condition and is considered a historically significant example of a pony truss road bridge. The bridge was added to the National Register of Historic Places on August 3, 1998.
Document 5: Mars: The large canyon, Valles Marineris (Latin for ``Mariner Valleys '', also known as Agathadaemon in the old canal maps), has a length of 4,000 km (2,500 mi) and a depth of up to 7 km (4.3 mi). The length of Valles Marineris is equivalent to the length of Europe and extends across one - fifth the circumference of Mars. By comparison, the Grand Canyon on Earth is only 446 km (277 mi) long and nearly 2 km (1.2 mi) deep. Valles Marineris was formed due to the swelling of the Tharsis area, which caused the crust in the area of Valles Marineris to collapse. In 2012, it was proposed that Valles Marineris is not just a graben, but a plate boundary where 150 km (93 mi) of transverse motion has occurred, making Mars a planet with possibly a two - tectonic plate arrangement.
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: Sevenmile Bridge: The Sevenmile Bridge is a Pratt deck truss bridge bringing a county road over the Rio Grande, southwest of Creede, Colorado, United States. It was designed by engineer King Burghardt and is unusual for its cantilevered ends. It was built in 1935; it then carried State Highway 149. It has also been known as Bridge over Rio Grande River. It was listed on the National Register of Historic Places in 1985.
Document 8: 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 9: 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 10: 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).
Document 11: South Canon Bridge: The South Canon Bridge is a truss footbridge spanning the Colorado River near Glenwood Springs, Colorado. It was built in 1915 by the Missouri Valley Bridge & Iron Co.. It was listed on the National Register of Historic Places (reference number 85000212) in 1985.).
Document 12: Laughery Creek Bridge: The Laughery Creek Bridge is a truss bridge on the border of Dearborn County, Indiana, and Ohio County, Indiana. It crosses Laughery Creek. This bridge was built in 1878. The Wrought Iron Bridge Company, a prolific late 19th-century bridge company, constructed the bridge. The bridge is seated on stone abutments. The deck surface is not original and is currently concrete. The bridge, nearly 300 feet in length, is a single span pin connected triple intersection Whipple through truss, and is the only example in the world of this truss type. The name bridge's nickname, "Triple Whipple Bridge" is a play on words. The double-intersection Pratt, which was called the Whipple truss configuration, was a far more common variation of the standard Pratt configuration. Since the Laughery Creek Bridge's members have three intersections instead of two, this gives rise to the "Triple Whipple" name. This bridge was listed on the National Register of Historic Places in 1976.
Document 13: 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 14: Deep River Camelback Truss Bridge: It spans the Deep River in North Carolina, United States between the hamlets of Gulf in Chatham County and Cumnock in Lee County in a quiet rural setting amid woods and farmlands on both sides of the river. It was originally constructed in 1901. The bridge is listed on the National Register of Historic Places. The bridge is open to pedestrian traffic only. Vehicles may use a replacement bridge located about a hundred yards east of the historic structure.
Document 15: 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.
ground_truth: about 5 to 6 million years ago
sub_queries: South Canon Bridge >> crosses Answer: Colorado River
when did Colorado River start to form the grand canyon Answer: about 5 to 6 million years ago