paragraph_text: The Messina Chasmata are the largest canyon or system of canyons on the surface of the Uranian moon Titania, named after a location in William Shakespeare's comedy Much Ado About Nothing. The 1492 km long feature includes two normal faults running NW–SE, which bound a down-dropped crustal block forming a structure called a graben. The graben cuts impact craters, which probably means that it was formed at a relatively late stage of the moon's evolution, when the interior of Titania expanded and its ice crust cracked as a result. The Messina Chasmata have only a few superimposed craters, which also implies being relatively young. The feature was first imaged by Voyager 2 in January 1986.

paragraph_text: São Pedro Apóstolo is a "freguesia" (civil parish) of Cape Verde. It covers the western part of the municipality of Ribeira Grande, on the island of Santo Antão.

paragraph_text: The Grand Canyon North Rim Headquarters is a historic district on the North Rim of the Grand Canyon in Grand Canyon National Park, Arizona. Established from 1926 through the 1930s, the district includes examples of National Park Service Rustic architecture as applied to employee residences, administrative facilities and service structures.

paragraph_text: The Marimbondo Dam is an embankment dam on the Grande River near Fronteira in Minas Gerais, Brazil. The dam serves an associated hydroelectric power plant with a installed capacity.

paragraph_text: Thistle is a ghost town in Spanish Fork Canyon in southeastern Utah County, Utah, United States. During the era of steam locomotives, the town's primary industry was servicing trains for the Denver and Rio Grande Western Railroad (often shortened to D&RG, D&RGW, or Rio Grande). The fortunes of the town were closely linked with those of the railroad until the changeover to diesel locomotives, when the town started to decline.

paragraph_text: SS "Grand Canyon State" (T-ACS-3) is a crane ship in ready reserve for the United States Navy. The ship was named for the state of Arizona, which is also known as the "Grand Canyon State".

paragraph_text: 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.

paragraph_text: The Palo Verde Dam (officially called the Palo Verde Diversion Dam) is a diversion dam on the Colorado River in La Paz County, Arizona, and Riverside County, California, in the southwestern United States, approximately northeast of Blythe. The dam is earthen and rockfill, built solely to divert water into irrigation canals serving the Palo Verde Irrigation District. It measures long at its crest, which is at an elevation of , and stands high above the riverbed, containing approximately of material. Construction of the dam, which began in 1956 and ended in 1958, was authorized by the U.S. Bureau of Reclamation. The dam was constructed to raise the water level of the river because the upstream Hoover and Davis Dams blocked sediment, causing significant degradation of the riverbed that hampered water diversion.

paragraph_text: The Palo Verde Biological Research Station is located in the Guanacaste Province of Costa Rica, and is one of the three research stations operated by the Organization for Tropical Studies (OTS). The Biological Research Station is located inside Palo Verde National Park. Palo Verde Biological Research Station is one of the foremost sites for ecological research on tropical dry forests, which constitute one of the most endangered forest types in the world.

paragraph_text: Byers Canyon is a short gorge on the upper Colorado River in Grand County, Colorado in the United States. The canyon is approximately 8 miles (13 km) long and is located in the headwaters region of the Colorado between Hot Sulphur Springs and Kremmling. U.S. Highway 40 passes through the canyon between Hot Sulphur Springs and Kremmling. The Union Pacific Railroad's Moffat Route also travels through the short canyon.

paragraph_text: 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.

paragraph_text: West of the Rocky Mountains lies the Intermontane Plateaus (also known as the Intermountain West), a large, arid desert lying between the Rockies and the Cascades and Sierra Nevada ranges. The large southern portion, known as the Great Basin, consists of salt flats, drainage basins, and many small north-south mountain ranges. The Southwest is predominantly a low-lying desert region. A portion known as the Colorado Plateau, centered around the Four Corners region, is considered to have some of the most spectacular scenery in the world. It is accentuated in such national parks as Grand Canyon, Arches, Mesa Verde National Park and Bryce Canyon, among others. Other smaller Intermontane areas include the Columbia Plateau covering eastern Washington, western Idaho and northeast Oregon and the Snake River Plain in Southern Idaho.

paragraph_text: Inniscarra Dam is a buttress dam located on the River Lee in County Cork, Ireland. Construction of the dam started in February 1953. It is owned and operated by the ESB Group. It has a generation capacity of 19 MW.

paragraph_text: Grand Canyon National Park, located in northwestern Arizona, is the 15th site in the United States to have been named a national park. The park's central feature is the Grand Canyon, a gorge of the Colorado River, which is often considered one of the Wonders of the World. The park, which covers 1,217,262 acres (1,901.972 sq mi; 4,926.08 km) of unincorporated area in Coconino and Mohave counties, received more than six million recreational visitors in 2017, which is the second highest count of all American national parks after Great Smoky Mountains National Park. The Grand Canyon was designated a World Heritage Site by UNESCO in 1979.

paragraph_text: 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).

paragraph_text: Box Canyon is a census-designated place (CDP) in Val Verde County, Texas, United States. The population was 34 at the 2010 census. This CDP was formed prior to the 2010 census from parts of the deleted Box Canyon-Amistad CDP.

paragraph_text: The Town of Cedaredge is a Home Rule Municipality in Delta County, Colorado, United States. The town population was 2253 at the 2010 United States Census. Cedaredge sits in the Surface Creek Valley beneath the southern slopes of the Grand Mesa, the largest mesa in the world. Its elevated vantage point affords southern views of the San Juan Mountains, the Black Canyon of the Gunnison National Park, and the communities of Delta, Olathe, and Montrose. Cedaredge is a small, agricultural community which produces beef cattle, apples, peaches, and wine from the region's few basic vineyards. Tourist attractions include Cedaredge Golf Club, Historic Pioneer Town, and an art gallery and craft store housed in a renovated apple packing shed. Regional sporting activities include camping, trophy hunting, hiking and Gold Medal fishing at more than 250 lakes on the Grand Mesa. During the winter locals partake in snowmobiling and Nordic skiing on the Mesa's trails. Powderhorn Resort is located north of Cedaredge and has ski terrain such as groomers, bumps, glades, and boulder fields, as well as two terrain parks.

paragraph_text: Canyon Creek is a hamlet in northern Alberta, Canada within the Municipal District of Lesser Slave River No. 124. It is located on Highway 2, approximately east of Grande Prairie.

paragraph_text: Hopi House is located on the South Rim of the Grand Canyon, within Grand Canyon National Park in the U.S. state of Arizona. Built in 1904 as concessioner facilities at the South Rim were being developed, it is the first of eight projects at the Grand Canyon that were designed by architect Mary Colter, along with Bright Angel Lodge, Hermit's Rest, Lookout Studio, Phantom Ranch, Desert View Watchtower, Colter Hall and Victor Hall, (the latter two being employee dormitories). Hopi House was built by the Fred Harvey Company as a market for Native American crafts, made by artisans on the site. The Hopi, as the historic inhabitants of the area, were chosen as the featured artisans, and the building was designed to closely resemble a traditional Hopi pueblo. Hopi House opened on January 1, 1905, two weeks before the El Tovar Hotel, located just to the west, was opened.

paragraph_text: 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, and some of the techniques were unproven. The torrid summer weather and lack of facilities near the site also presented difficulties. Nevertheless, Six Companies turned over the dam to the federal government on March 1, 1936, more than two years ahead of schedule.

Question: When did the river on which the Palo Verde Dam is located start forming the Grand Canyon?
Answer: about 5 to 6 million years ago