ROCKY MOUNTAINS

byname The Rockies, mountain range that is a major component of the great upland system of western North America, extending from northern Alberta, Can., southward through the western United States to Mexico, a distance of some 3,000 miles (4,800 km). It is bounded by the Great Plains on the east and by the ridges and plateaus of the Western Intermontane Region, which includes the Basin and Range Province, on the west. The width of the system varies from 70 to 400 miles (110 to 650 km) and the elevation from 5,000 feet (1,500 m) to 14,433 feet (4,399 m) at Mount Elbert, Colorado, the highest point in the Rockies. In the Late Cretaceous Period (97.5 to 66.4 million years ago), the Laramide orogeny (mountain-building episode) uplifted the young folded mountains of the Rockies, which were later subjected to further uplifting and glaciation. Physiographically, the Rockies comprise two distinct divisions, eastern and western. The eastern division has two massive uplifts, the 300-mile- (480-kilometre-) long Front Range of Colorado and the central Arizona uplift (of similar extent); the rest of the ranges are smaller and quite uniform in size, about 60 miles (95 km) long and 15 miles (25 km) wide. Layers of sedimentary rocks in the ranges of the eastern division are relatively thin, varying in thickness from a few feet to 6,000 to 7,000 feet (1,800 to 2,100 m), and are mostly uplifted in place with little folding or faulting. The western division is very different, being characterized by a series of parallel ridges created by extensive thrust and block faulting and folding; the sedimentary rockbeds of these ridges have a thickness of more than 40,000 feet (12,000 m) in places. The western division's main subdivisions are the Canadian and the northwestern Montana Rockies. Some of North America's major rivers, such as the Missouri, Rio Grande, Columbia, and Colorado, originate in the Rockies, which also form the Continental Divide separating rivers flowing toward the Gulf of Mexico and Atlantic Ocean in the east from those flowing toward the Pacific Ocean in the west. The snow line (the lower margin of perennial snowfields) in the Rockies is at about 13,000 feet (4,000 m) in the southern ranges and 8,000 feet (2,500 m) in the northern ranges. Rocky Mountain flora includes white spruce, juniper, aspen, fir, pine, and alpine meadow grasses. The mountains' fauna includes grizzly bear, brown bear, wapiti (elk), mule deer, Rocky Mountain goat, bighorn sheep, and cougar. The Rocky Mountain states of Idaho, Nevada, Utah, New Mexico, Arizona, Colorado, Montana, and Wyoming have rich deposits of copper, iron ore, silver, gold, lead, zinc, phosphate, potash, and gypsum; these states are also substantial producers of coal, natural gas, and petroleum. In the Rocky Mountains are found almost all of the United States' molybdenum, beryllium, and uranium. Other economic activities on the mountain slopes and valleys are ranching, lumbering, and tourism. Rocky Mountain, Yellowstone, and Grand Teton national parks in the United States are major recreational facilities. Physical features of western North America. byname the Rockies, mountain range forming the backbone of the great upland system that dominates the western North American continent. Generally, the ranges included in the Rockies stretch from northern Alberta and British Columbia southward to New Mexico, a distance of some 3,000 miles (4,800 kilometres). In places the system is 300 or more miles wide. Limits are mostly arbitrary, especially in the far northwest, where mountain systems such as the Brooks Range of Alaska are sometimes included. The Rockies are bordered on the east by the Great Plains and on the west by the Interior Plateau and Coast Mountains of Canada and the Columbia Plateau and Basin and Range Province of the United States. The Rocky Mountains include at least 100 separate ranges, which are generally divided into four broad groupings: the Canadian Rockies and Northern Rockies of Montana and northeastern Idaho; the Middle Rockies of Wyoming, Utah, and southeastern Idaho; the Southern Rockies, mainly in Colorado and New Mexico; and the Colorado Plateau in the Four Corners region of Utah, Colorado, New Mexico, and Arizona. These four subdivisions differ from each other in terms of geology (origin, ages, and types of rocks) and physiography (landforms, drainage, and soils), yet they share the physical attributes of high elevations (many peaks exceeding 13,000 feet [4,000 metres]), great local relief (typically 5,000 to 7,000 feet in vertical difference between the base and summit of ranges), shallow soils, considerable mineral wealth, spectacular scenery from past glaciation and volcanic activity, and common trends in climate, biogeography, culture, economy, and exploration. Additional reading Two nontechnical, abundantly illustrated descriptions of the Rocky Mountains are William S. Ellis and Dick Durrance II, The Majestic Rocky Mountains (1976); and Bryce S. Walker et al., The Great Divide (1973, reissued 1985), covering the landforms, plant life, and early exploration of the American Rockies. The mountains are also treated in Mel Griffiths and Lynnell Rubright, Colorado: A Geography (1983); and American West, The Magnificent Rockies: Crest of a Continent (1973). Dennis Glick, Mary Carr, and Bert Harting, An Environmental Profile of the Greater Yellowstone Ecosystem (1991), compiles baseline information on the ecological processes and components of the greater Yellowstone ecosystem and discusses how the ecosystem's future is affected by current and proposed resource development plans. David V. Harris and Eugene P. Kiver, The Geologic Story of the National Parks and Monuments, 4th ed. (1985), chapters 811, covers the geologic history and special features of U.S. parks and monuments in the northern, middle, and southern Rockies and on the Colorado Plateau. Lawrence M. Ostresh, Jr., Richard A. Marston, and Walter M. Hudson, Wyoming Water Atlas (1990), although specifically about Wyoming water resources, treats issues that are typical throughout the Rocky Mountain region. Richard A. Marston