Rocky Mountains
Rocky Mountains major mountain system of W North America and easternmost belt of the North American cordillera, extending more than 3,000 mi (4,800 km) from central N.Mex. to NW Alaska; Mt. Elbert (14,431 ft/4,399 m) in Colorado is the highest peak. The Rockies are located between the Great Plains on the east (from which they rise abruptly for most of their length) and a series of broad basins and plateaus on the west.
The mountains form the Continental Divide, separating rivers draining to the Atlantic and Arctic oceans from those draining to the Pacific. The major Atlantic-bound rivers rising in the Rockies include the Rio Grande, Arkansas, Platte, Yellowstone, Missouri, and Saskatchewan. Those draining to the Arctic include the Peace, Athabasca, and Liard rivers. Flowing to the Pacific Ocean are the Colorado, Columbia, Snake, Fraser, and Yukon rivers.
Formation
The Rockies were formed in the Mesozoic and Early Cenozoic eras during the Cordilleran orogeny. They are geologically complex, with remnants of an ancestral Rocky Mt. system and evidence that uplift, which involved almost all mountain-building processes (see mountain ), occurred as a series of pulses over millions of years. The mountains have since been eroded to expose ancient crystalline cores flanked by thick upturned layers of sedimentary rocks. Glaciers and snowfields, which cover portions of the northern ranges and the high peaks of the south, were at one time more extensive; throughout the system the erosional features of alpine glaciation are apparent.
Topography
Topographically, the Rockies are usually divided into five sections: the Southern Rockies, Middle Rockies, Northern Rockies (all in the United States), the Rocky Mountain system of Canada, and Brooks Range in Alaska. The Wyoming Basin, the system's principal topographic break, is sometimes considered a sixth section.
The Southern Rockies, in New Mexico, Colorado, and S Wyoming, are dominated by two north-south belts of folded mountains that have been eroded to expose cores of Precambrian rocks rimmed by younger sedimentary rocks. The eastern belt comprises the Laramie, Medicine Bow, and Wet Mts. and the Front Range. The principal ranges of the western belt are the Park, Gore, Mosquito, Sawatch, and Sangre de Cristo. Between the two belts are three basins known as the North, South, and Middle "parks." To the southwest are the San Juan Mts., a nonlinear group of uplands composed mainly of volcanic rocks. The Southern Rockies are the system's highest section and include many peaks above 14,000 ft (4,267 m), among them Mt. Elbert and Mt. Massive (14,418 ft/4,395 m), both in the Sawatch Mts.
The Middle Rockies, chiefly in NE Utah and W Wyoming, lie N of the Southern Rockies and are separated from them by the Wyoming Basin. The ranges of this section are generally lower and less continuous than those to the south. The principal parts are the Wasatch and Teton ranges (which are both great tilted fault blocks), the Yellowstone Plateau and Absaroka Range (both developed on volcanic rocks), the Bighorn, Beartooth, Owl Creek, and Uinta Mts., and the Wind River Range (all broad folded mountains). All of these component sections have been eroded down to their Precambrian cores and are rimmed by Paleozoic and Mesozoic sedimentary rocks. The highest peaks of the Middle Rockies are Gannet Peak (13,785 ft/4,202 m) in the Wind River Range and Grand Teton (13,766 ft/4,196 m) in the Teton Range.
The Northern Rockies, in NE Washington, N and central Idaho, NW Wyoming, and W Montana extend N from Yellowstone National Park to the U.S.-Canadian border. They are composed of the Clearwater and Salmon River Mts., the Sawtooth and Lost River ranges (all of which developed in the batholith of central Idaho), and the Bitterroot Range along the Idaho-Mont. line. In the east are the Front Ranges of Montana. A series of north-south trending ranges separated by narrow trenches and valleys occupies most of N Montana and the Idaho panhandle. Two especially distinctive trenches are the Rocky Mountain Trench, which extends NW from Flathead Lake, and the Purcell Trench, which extends N from Coeur d'Alene Lake. The Okanagan Highlands, in NE Washington, form the western edge of the Northern Rockies. The peaks of the Northern Rockies are generally lower than those to the south; among the highest are Borah Peak (12,655 ft/3,857 m) and Leatherman Peak (12,230 ft/3,728 m) in the Lost River Range.
The Rocky Mt. system of Canada is composed of two major sections: the high rugged peaks of the Canadian Rockies proper, to the east, and the Columbia Mts. group on the west. The Canadian Rockies are located along the British Columbia-Alberta border and include Mt. Robson (12,972 ft/3,954 m; highest peak of the Rocky Mts. in Canada), Mt. Columbia (12,295 ft/3,748 m), and Mt. Forbes (11,902 ft/3,628 m). The prominent, wide-floored Rocky Mountain Trench, west of the crest line, continues c.800 mi (1,290 km) into Canada from Montana and is drained by the headwaters of the Peace River and by sections of the Fraser, Columbia, and Kootenay rivers. The Purcell Trench to the west also crosses into Canada and joins the Rocky Mountain Trench c.200 mi (320 km) north of the border. Farther to the west is the Columbia Mts. group, which includes the Selkirk, Purcell, Monashee, and Cariboo Mts. The Rockies continue into the Yukon Territory and Northwest Territories as the Mackenzie, Richardson, and Franklin Mts. In N Alaska, the Brooks Range, a cold and treeless region rising to Mt. Chamberlin (9,020 ft/2,749 m), forms the northernmost section of the Rocky Mts.
Economy and Natural Resources
Exploitable mineral deposits (lead, zinc, copper, silver, gold) are sparsely dispersed throughout the entire system. The principal mining centers are Leadville and Cripple Creek, Colo.; the Butte-Anaconda district of Montana; Coeur d'Alene, Idaho; and the Kootenay Trail region of British Columbia. In the 1970s oil shale found in the Rocky Mt. area led to an oil industry that spurred city and state growth, especially in Colorado; by the mid-1980s, the industry was already in decline.
Vast forests, largely under government control and supervision, are a major natural resource. Lumbering and other forestry activities are limited mainly to Montana, Idaho, and British Columbia, where commercially valuable stands are most abundant and accessible.
The Rockies are a year-round recreational attraction, and the surrounding states have seen a boom in vacation-housing construction and, thus, population increases since the late 1970s. The U.S. national parks in the system include Rocky Mountain, Yellowstone, Grand Teton , and Glacier . Rocky Mountain National Park (265,723 acres/107,580 hectares) is in central Colorado. Straddling the Continental Divide in the Front Range of the Southern Rockies, the park features more than 100 peaks towering over 11,000 ft (3,353 m). The highest is Longs Peak (14,255 ft/4,345 m). The park, which was authorized in 1915, also contains many lakes and waterfalls. (See also National Parks and Monuments , table.) In Canada are Jasper , Banff , Yoho , Glacier , Kootenay , Mount Revelstoke , and Waterton Lakes national parks.
Passes and Explorers
The Rockies were traversed by westward-bound pioneers; the principal U.S. pass across the mountains is South Pass (alt. c.7,550 ft/2,301 m) at the southern end of the Wind River Range, SW Wyoming, which links the Wyoming Basin and the Great Plains with the basins and plateaus W of the Rockies. This pass was followed by the Oregon and Mormon trails. The Santa Fe Trail skirted the southern end of the Rockies. In Canada the important passes are Kicking Horse (alt. 5,539 ft/1,688 m), which carries the Trans-Canada Highway, Crowsnest Pass, and Yellowhead Pass.
Explorers of the U.S. Rockies have included Vasquez de Coronado (1540), Meriwether Lewis and William Clark (1804-6), Zebulon Pike (1806-7), Stephen Long (1819-20), Benjamin Bonneville (1832-35), John Frémont (1843-44), Isaac Stevens (1853), John W. Powell (1868), and Ferdinand Hayden (1871). Leading Canadian explorers were sieur de la Vérendrye (1738-39), Sir Alexander Mackenzie (1792-93), David Thompson (1799-1803), and Simon Fraser (1803-7).
Bibliography
See W. W. Atwood, The Rocky Mountains (1945); P. Eberhart and P. Schmuck, The Fourteeners, Colorado's Great Mountains (1970); The Magnificent Rockies, pub. by American West (1973); D. Lavender, The Rockies (1981); H. Chronic, Time, Rocks, and the Rockies (1984); J. McPhee, Rising From the Plains (1986).
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