Northwestern Arizona is part of the arid Colorado Plateau. Sedimentary rocks here were uplifted horizontally. The dry environment made them susceptible to erosion.
About four million years ago, the Colorado River changed its course and began to cut through the layers of the present-day Grand Canyon. Winds, rain and runoff further eroded canyon walls and created side canyons.
Although Arizona is known for dry, hot weather, ice plays a major role in canyon formation. When water seeps into cracks in the rock and freezes during the winter, it expands, pushing the rock apart.
The Grand Canyon is an important resource for geologists. Its layers hold fossils and rocks that reveal three of the earth's four geological eras.
The Grand Canyon is young compared with the layers of rock represented in its walls. The youngest layer, Kaibab limestone, is 250 million years old. The oldest, Vishnu schist, is 2.6 billion years old.
These layers comprise the walls of the Grand Canyon, which average 4,000 feet deep and run for more than 277 miles.