The Grand Canyon in a moonlit night. Polaris, the North Star, and the rest of constellation Ursa Minor (the Little Bear) are visible through passing high clouds on the upper right. On the left is part of the constellation Draco. The city of St. George in Utah illuminates the clouds on the left. The Grand Canyon in northern Arizona is the longest canyon on the Earth, a steep-sided gorge carved by the Colorado River steadily in about 17 million year time span. The canyon is 446 km long, ranges in width from about 6 to 29 km and attains a depth of more than 1.6 km or about a mile.