The Colorado River is a river in the southwestern United States and northwestern Mexico, approximately 1,450 mi long, draining a part of the arid regions on the western slope of the Rocky Mountains. The natural course of the river flows into the Gulf of California, but the heavy use of the river as an irrigation source for the Imperial Valley has desiccated the lower course of the river in Mexico such that it no longer consistently reaches the sea.
Grand Canyon National Park is one of America's oldest national parks and is located in Arizona. Within the park lies the Grand Canyon, a gorge of the Colorado River, considered to be one of the major natural wonders of the world. The park covers 1,902 mi².
Most visitors to the park come to the South Rim, arriving on Arizona Highway 64. The Highway enters the park through the South Entrance, near Tusayan, Arizona, and heads eastward, leaving the park through the East Entrance. Park headquarters are at Grand Canyon Village, a short distance from the South Entrance, being also the center of the most popular viewpoints. Some thirty miles of the South Rim are accessible by road. A much smaller venue for tourists is found on the North Rim, accessed by Arizona Highway 67. There is no connection by road between the two, except via the Navajo Bridge, entailing a five-hour drive. The rest of the Grand Canyon is extremely rugged and remote, although many places are accessible by pack trail and backcountry roads.
The Grand Canyon itself—really an extensive system of tributary canyons— is neither the largest or deepest canyon in the world, but is valued for the combination of large size, depth, and the exposed layering of colorful rocks dating back to Precambrian times. It was created by erosion from the Colorado River and its tributaries.