portal: Arizona

The Grand Canyon is a steep-sided gorge carved by the Colorado River in the United States state of Arizona. It is largely contained within the Grand Canyon National Park  one of the first national parks in the United States. President Theodore Roosevelt was a major proponent of preservation of the Grand Canyon area, and visited on numerous occasions to hunt and enjoy the scenery.

Prior to European emigration, the area was inhabited by Native Americans who built settlements within the canyon and its many caves. The Pueblo people considered the Grand Canyon ("Ongtupqa" in Hopi language) a holy site and made pilgrimages to it.Fact: date=November 2007 The first European known to have viewed the Grand Canyon was García López de Cárdenas from Spain, who arrived in 1540. In 1869, Major John Wesley Powell, a one-armed Civil War veteran with a thirst for science and adventure, made the first recorded journey through the canyon on the Colorado River. Powell referred to the sedimentary rock units exposed in the canyon as "leaves in a great story book".Fact: date=April 2008

Geography

The Grand Canyon is a massive rift 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. The Grand Canyon is unmatched throughout the world for the vistas it offers to visitors on the rim. It is not the deepest canyon in the world — Cotahuasi Canyon (11598 feet or 3535 m) and Colca Canyon (10499 feet or 3200 m), both in Arequipa, Peru, and Hell's Canyon (7,993 feet or2436 m) on the Oregon-Idaho border, are all deeper — but Grand Canyon is known for its overwhelming size and its intricate and colorful landscape. Geologically it is significant because of the thick sequence of ancient rocks that are beautifully 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 building events later moved these sediments thousands of feet upward and created the Colorado Plateau. The higher elevation has also 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, and the north-south trending Kaibab Plateau that Grand Canyon bisects is over a thousand feet higher at the North Rim (about 1,000 ft/300 m) than at the South Rim. The fact that the Colorado River flows in a curve around the higher North Rim part of the Kaibab Plateau and closer to the South Rim part of the plateau is also explained by this asymmetry. Ivo Lucchitta of the U.S. Geological Survey first suggested that, as the Colorado River developed before significant erosion of the region, it naturally found its way across or around the Kaibab Uplift by following a "racetrack" path to the south of the highest part of the plateau. Almost all runoff from the North Rim (which also gets more rain and snow) flows toward the Grand Canyon, while much of the runoff on the plateau behind the South Rim flows away from the canyon (following the general tilt). The result is deeper and longer tributary washes and canyons on the north side and shorter and steeper side canyons on the south side.