The Grand Canyon, cut out by the Colorado River over a period of 15 million years in the northwest comer of Arizona, is the largest land gorge in the world. It is 4 to 13 miles (6.4 to 21 kilometers) wide at its brim, 4,000 to 5,500 feet (1,219 to 1,676 meters) deep, and 217 miles (349 kilometers) long, extending from the mouth of the Little Colorado River to Grand Wash Cliffs (and 277 miles, 600 feet or 445.88 kilometers if Marble Canyon is included).
However, it is not the deepest canyon in the United States; that distinction belongs to Kings Canyon, which runs through the Sierra and Sequoia National Forests near East Fresno, California, with its deepest point being 8,200 feet (2,500 meters). Hell's Canyon of the Snake River between Idaho and Oregon is the deepest United States canyon in low-relief territory. Also called the Grand Canyon of the Snake, it plunges 7,900 feet (2,408 meters) down from Devil Mountain to the Snake River. (The Handy Science Answer Book, compiled by the Science and Technology department of the Carnegie Library of Pittsburgh)