The Milky Way above the Grand Canyon in northern Arizona. Constellations Cygnus, Cepheus, and Cassiopeia appear in the sky and the Andromeda Galaxy is near the top. The Grand Canyon, a World Heritage Site in northern Arizona, USA, 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 (a mile). Date: Nov. 2012