![]() ![]() Some of these thrust sheets have moved 20 to 30 miles (32 to 48 km) to their present positions. ![]() The ranges of the Canadian and Northern Rockies were created when thick sheets of Paleozoic limestones were thrust eastward over Mesozoic rocks during the mountain-building episode called the Laramide Orogeny (65 to 35 million years ago). This structural depression, known as the Rocky Mountain Geosyncline, eventually extended from Alaska to the Gulf of Mexico and became a continuous seaway during the Cretaceous Period (about 145 to 66 million years ago). These ranges formed along the eastern edge of a region of carbonate sedimentation some 17 miles (27 km) thick, which had accumulated from the late Precambrian to early Mesozoic time (i.e., between about 1 billion and 190 million years ago). The Northern Rockies include the Lewis and Bitterroot ranges of western Montana and northeastern Idaho. The Canadian Rockies include the Mackenzie and Selwyn mountains of the Yukon and Northwest Territories (sometimes called the Arctic Rockies) and the ranges of western Alberta and eastern British Columbia. 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 ), 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. 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. 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. Limits are mostly arbitrary, especially in the far northwest, where mountain systems such as the Brooks Range of Alaska are sometimes included. In places the system is 300 or more miles wide. 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 km). Rocky Mountains, byname the Rockies, mountain range forming the cordilleran backbone of the great upland system that dominates the western North American continent. SpaceNext50 Britannica presents SpaceNext50, From the race to the Moon to space stewardship, we explore a wide range of subjects that feed our curiosity about space!.Learn about the major environmental problems facing our planet and what can be done about them! Saving Earth Britannica Presents Earth’s To-Do List for the 21st Century. ![]() Britannica Beyond We’ve created a new place where questions are at the center of learning. ![]() 100 Women Britannica celebrates the centennial of the Nineteenth Amendment, highlighting suffragists and history-making politicians.COVID-19 Portal While this global health crisis continues to evolve, it can be useful to look to past pandemics to better understand how to respond today.Student Portal Britannica is the ultimate student resource for key school subjects like history, government, literature, and more.This Time in History In these videos, find out what happened this month (or any month!) in history.#WTFact Videos In #WTFact Britannica shares some of the most bizarre facts we can find.Demystified Videos In Demystified, Britannica has all the answers to your burning questions.Britannica Explains In these videos, Britannica explains a variety of topics and answers frequently asked questions.Britannica Classics Check out these retro videos from Encyclopedia Britannica’s archives. ![]()
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