GRAND CANYON

immense canyon cut by the Colorado River into the high-plateau region of northwestern Arizona, U.S., noted for its fantastic shapes and coloration. The Grand Canyon lies in the southwestern portion of the Colorado Plateau, which is a large area of the southwestern United States consisting essentially of horizontal, layered rocks and lava flows. The broad, intricately sculptured chasm of the canyon contains between its outer walls a multitude of imposing peaks, buttes, gorges, and ravines. It ranges in width from about 0.1 to 18 miles (0.2 to 29 km) and extends in a winding course from the mouth of the Paria River, near Lees Ferry and the northern boundary of Arizona, to Grand Wash Cliffs, near the Nevada line, a distance of about 277 miles (446 km). Its greatest depths lie more than a mile (some 6,000 feet [1,800 metres]) below its rim. The canyon includes many tributary side canyons and surrounding plateaus. The deepest and most impressively beautiful section, 56 miles (90 km) long, is within the central part of Grand Canyon National Park, which encompasses the river's length from Lake Powell (formed by Glen Canyon Dam in 1963) to Lake Mead (formed by Hoover Dam in 1936). In its general colour, the canyon is red, but each stratum or group of strata has a distinctive hue-buff and gray, delicate green and pink, and, in its depths, brown, slate-gray, and violet. At approximately 8,200 feet (2,500 metres) above sea level, the North Rim is some 1,200 feet (350 metres) higher than the South Rim. Additional reading Jeremy Schmidt, The Grand Canyon National Park: A Natural History Guide (1993); Ann Zwinger, Downcanyon: A Naturalist Explores the Colorado River Through the Grand Canyon (1995); and Stephen R. Whitney, A Field Guide to the Grand Canyon, 2nd ed. (1996), cover the natural history of the park and present its flora and fauna. Barbara J. Morehouse, A Place Called Grand Canyon (1996), discusses the physical and cultural history of the area from early Native-American presence to modern times. Donald L. Baars, Rex C. Buchanan, and John R. Charlton, The Canyon Revisited: A Rephotography of the Grand Canyon, 1923/1991 (1994), combines photos taken by the Birdseye expedition of 1923 with photographs taken in 1991.