The Colorado River is a major North American river draining much of the southwestern United States and a small part of Northwestern Mexico. It originates at the Continental Divide at La Poudre Pass in the Rocky Mountain National Park of north-central Colorado and flows generally southwest and then south for 1,450 miles (2,334 km) to the Gulf of California also known as The Sea of Cortez. The river flows through Colorado, Utah, and Arizona and serves as the boundary between Arizona and Nevada and California. It also separates the Mexican states of Sonora and Baja California.
Tributaries include the Green River, the Gunnison River, the Dolores River, the San Juan River, and Little Colorado River. The entire drainage basin, including parts of Wyoming and New Mexico, consists of 244,000 square miles (632,000 km 2 )—about 7 per cent of the United States. In its course to the sea, the Colorado drops nearly 2 1/2 miles (4 km) and passes through sparsely populated arid and semiarid land, mainly plateaus and deserts. In much of its middle course it flows through deep canyons with sheer walls, the most notable of which is the Grand Canyon—217 miles (349 km) long and 4 to 18 miles (6,400 m to 29 km) wide, with an average depth of 1 mile (1,600 m).