The Grand Canyon is a dramatic deep gorge, carved by the
Colorado River in the state of Arizona. The Grand Canyon
ranges in width from 4 to 18 miles (6.4 to 29km) and
averages a mile (1.6km) deep. Scientists now think the Grand
Canyon was carved over a period 17 million years. Nearly two
billion years of Earth's history have been exposed in the
layered canyon walls.