The Grand Canyon is a 277-mile-long canyon carved by the Colorado River in Arizona. The Colorado River and its tributaries cut their channels through layer after layer of rock while the Colorado Plateau was uplifted, and much of the canyon has been drained of water. For thousands of years, the area was continuously inhabited by Native Americans, who built settlements within the canyon and its many caves. In 1540, the Spanish explorer Garcia Lopez de Cardenas explored the canyon, which became a US national park in 1919.