The Grand Canyon is a colorful, steep-sided gorge, carved by the Colorado River, in northern Arizona. The canyon, considered to be among the major natural wonders of the world, is largely contained in the Grand Canyon National Park - one of the first national parks in the United States. President Theodore Roosevelt was a major proponent of the Grand Canyon area, visiting on numerous occasions to hunt mountain lions and enjoy the breathtaking scenery.
The canyon, created by the Colorado River cutting a channel over millions of years, is about 350 kilometers long, ranges in width from 6 to 29 kilometers and attains a depth of more than 1,600 m. The details of its development are still somewhat controversial. The most likely scenario is that a large lake overflowed the Kaibab Plateau about 5 million years ago, following the route taken by the Little Colorado River up to 70 million years ago. That accounts for the narrow lower (western) canyon and the much wider upper (eastern) canyon, as well as several other lines of evidence.
Aside from casual sightseeing from the South Rim, whitewater rafting and hiking are especially popular. The floor of the valley is accessible by hiking, muleback, or by boat or raft from upriver. Commercially organized rafting trips, using 35-foot, 15 person "baloney boats" equipped with outboard engines, make the trip from Lee's Ferry to Diamond Creek in about six days. 18-foot rafts and dories powered only with oars and paddles, and take over two weeks to complete the journey. Sightseers are also carried over the canyon by helicopter.