The Rockies are a shallow-slab orogeny, not a single wall
North America’s largest mountain system, the Rockies run about 3,000 miles—4,800 kilometres—from northern Western Canada to New Mexico. They rose mainly 55 to 80 million years ago in the Laramide orogeny, when shallow subduction bulged a broad highland belt instead of a narrow coastal chain.
Later uplift and glaciation carved today’s peaks. Colorado holds most of the highest summits and averages about 6,800 feet above sea level, and public parks and forests protect much of the range for hiking, climbing, fishing, hunting, skiing and snowmobiling. The English name copies the Plains Cree asinîwaciy, rocky mountain, which first reached European records as montagnes de Roche in the 1752 journal of Jacques Legardeur de Saint-Pierre.
Common definitions run from the Liard River in British Columbia to the headwaters of the Pecos in New Mexico, with widths between 110 and 480 kilometres. The eastern front springs abruptly from the Interior Plains in ranges such as the Sangre de Cristo, Colorado’s Front Range, Wyoming’s Wind River and Big Horn mountains, Montana’s Absaroka-Beartooth, South Dakota’s Black Hills and Alberta’s Clark Range. Central ranges include the La Sal, Uinta and Teton.
On the western side stand the Wasatch near Salt Lake City, the San Juans, the Bitterroots on the Idaho–Montana line and Idaho’s Sawtooths, cut off from ranges farther west by the Great Basin and Columbia Plateau. In Canada the western boundary is the vast Rocky Mountain Trench, running the length of British Columbia from the Kechika Valley by the Liard to the Lake Koocanusa valley in north-western Montana.
Canadian geographers define their Rockies as everything south of the Liard and east of the trench, split into the Muskwa, Hart and Continental ranges. Northern chains such as Yukon’s Selwyn, Mackenzie and Richardson mountains and Alaska’s Brooks Range fall outside the range for Canada’s geological survey, while America’s Geological Society treats them as Arctic Rockies.
Source: Rocky Mountains
