Grand Canyon

The South Rim of the Grand Canyon in Arizona, USA. Erosion has created dramatic configurations in the sedimentary rock formations in and around the gorge.

Formed over millions of years by the Colorado River cutting through layers of sandstone, shale, limestone, and gneiss, the USA's Grand Canyon is one of the most spectacular natural features in the world. The variation in climate at different levels supports a wide variety of wildlife and vegetation.

Sunrise over the Grand Canyon, Arizona. Reaching depths of over 1.6 km/1 mi, the Grand Canyon National Park is one of the most popular in the US national park system, with many trails for hiking, mule riding, and trips on the river by boat or raft. The varying tones of the different layers of rock change with the light throughout the day.

Gorge in northwestern Arizona, USA, containing the Colorado River. It is 350 km/217 mi long, 6-29 km/4-18 mi wide, and reaches depths of over 1.7 km/1.1 mi. The gorge cuts through a multicoloured series of rocks - mainly limestones, sandstones, and shales, and ranging in age from the Precambrian to the Cretaceous - and various harder strata stand out as steps on its slopes. It is one of the country's most popular national parks and around 5 million tourists visit it each year.

Protected since 1893, and accessible by rail since 1901, the Grand Canyon was made a national monument in 1908, a national park in 1919, and a World Heritage Site in 1979. Most visitors approach the canyon via the more accessible South Rim; the North Rim is around 300-500 m/1,000-1,500 ft higher, and is closed during the winter. The national park has an area of 4,931 sq km/1,904 sq mi, and is bounded by Glen Canyon to the east and Lake Mead to the west. On its way through the canyon the Colorado River drops 670 m/2,200 ft through dozens of rapids.

The canyon has been formed in the past 6-8 million years by the river cutting through generally sedimentary strata; but it reveals some of the oldest rock on the earth's surface, over 2 billion years old, at the bottom of hundreds of layers of sandstone, shale, travertine, schist, granite, and other rocks.

Lived in for hundreds of years by various American Indian groups, the area has over 500 ruin sites. The Spanish explorer Francisco Vasquez de Coronado became the first European to see the canyon in 1540; the US geologist John Wesley Powell travelled down the river through the gorge in 1869.

Marble Canyon, to the northeast, is now part of the park. The Coconino Plateau lies to the south, the Kaibab and other plateaux to the north. Havasu Canyon, on the Havasu Creek, enters from the south near the canyon's west end; this is home to the Havasupai reservation, with a population (1990 est) of 400.

The US National Park Service aims to ban all cars, buses, and motor homes on the Grand Canyon overlooks by 2003. The project will improve the South Rim which attracts 90% of the tourists to the area who on some days bring about 6,000 cars.

The Grand Canyon-Parashant National Monument, protecting the north rim of the canyon and including over 400,000 ha/1,000,000 acres of public land, was formed in 2000.