Great Plains

The Great Plains are a broad expanse of flatland in North America. The region is located just to the east of the Rocky Mountains, much of it covered in prairie, steppe, and grassland. They are the western part of the Interior Plains, which include the mixed grass prairie, the tallgrass prairie between the Great Lakes and Appalachian Plateau, and the Taiga Plains and Boreal Plains ecozones in Northern Canada. "Great Plains", or Western Plains, is also the ecoregion of the Great Plains or alternatively the western portion of the Great Plains.

The Great Plains lie across both the Central United States and Western Canada, encompassing:

Most or all of the U.S. states of Kansas, Nebraska, North Dakota and South Dakota;
Eastern parts of the U.S. states of Colorado, Montana, and Wyoming;
Parts of the U.S. states of New Mexico, Oklahoma, Texas;
Sometimes western parts of Iowa, Minnesota, and Missouri;
The southern portions of the Canadian provinces of Alberta, Saskatchewan and Manitoba.

Usage

The term "Great Plains" is used in the United States to describe a sub-section of the even more vast Interior Plains physiographic division, which covers much of the interior of North America. It also has currency as a region of human geography, referring to the Plains Indians or the Plains states.^{[citation needed]}

In Canada the term is rarely used; Natural Resources Canada, the government department responsible for official mapping, treats the Interior Plains as one unit consisting of several related plateaus and plains. There is no region referred to as the "Great Plains" in the Atlas of Canada.^[2] In terms of human geography, the term prairie is more commonly used in Canada, and the region is known as the Canadian Prairies, Prairie Provinces or simply "the Prairies".^{[citation needed]}

The North American Environmental Atlas, produced by the Commission for Environmental Cooperation, a North American Free Trade Agreement (NAFTA) agency composed of the geographical agencies of the Mexican, American, and Canadian governments, uses the "Great Plains" as an ecoregion synonymous with predominant prairies and grasslands rather than as physiographic region defined by topography.^[3] The Great Plains ecoregion includes five sub-regions: Temperate Prairies, West-Central Semi-Arid Prairies, South-Central Semi-Arid Prairies, Texas Louisiana Coastal Plains, and Tamaulipas-Texas Semi-Arid Plain, which overlap or expand upon other Great Plains designations.^[4]

Extent

The region is about 500 mi (800 km) east to west and 2,000 mi (3,200 km) north to south. Much of the region was home to American bison herds until they were hunted to near extinction during the mid/late-19th century. It has an area of approximately 500,000 sq mi (1,300,000 km²). Current thinking regarding the geographic boundaries of the Great Plains is shown by this map at the Center for Great Plains Studies, University of Nebraska–Lincoln.^[1] This definition, however, is primarily ecological, not physiographic. The Boreal Plains of Western Canada are physiographically the same, but differentiated by their tundra and forest (rather than grassland) appearance.

The term "Great Plains", for the region west of about the 96th meridian west and east of the Rocky Mountains, was not generally used before the early 20th century. Nevin Fenneman's 1916 study Physiographic Subdivision of the United States^[5] brought the term Great Plains into more widespread usage. Before that the region was almost invariably called the High Plains, in contrast to the lower Prairie Plains of the Midwestern states.^[6] Today the term "High Plains" is used for a subregion of the Great Plains.^[7] The term still remains little-used in Canada compared to the more common, "prairie".

Geography

The Great Plains are the westernmost portion of the vast North American Interior Plains, which extend east to the Appalachian Plateau. The United States Geological Survey divides the Great Plains in the United States into ten physiographic subdivisions:

Missouri Coteau or Missouri Plateau (which also extends into Canada), glaciated – east central South Dakota, northern and eastern North Dakota and northeastern Montana;
Coteau du Missouri, unglaciated – western South Dakota, northeastern Wyoming, southwestern North Dakota and southeastern Montana;
Black Hills – western South Dakota;
High Plains – southeastern Wyoming, southwestern South Dakota, western Nebraska (including the Sand Hills), eastern Colorado, western Kansas, western Oklahoma, eastern New Mexico, and northwestern Texas (including the Llano Estacado and Texas Panhandle);
Plains Border – central Kansas and northern Oklahoma (including the Flint, Red and Smoky Hills);
Colorado Piedmont – eastern Colorado;
Raton section – northeastern New Mexico;
Pecos Valley – eastern New Mexico;
Edwards Plateau – south central Texas; and
Central Texas section – central Texas.

Further to this can be added Canadian physiographic sub-regions such as the Alberta Plain, Cypress Hills, Manitoba Escarpment (eastward), Manitoba Plain, Missouri Coteau (shared), Rocky Mountain Foothills (eastward), and Saskatchewan Plain.^[8]

The Great Plains consist of a broad stretch of country underlain by nearly horizontal strata extending westward from the 97th meridian west to the base of the Rocky Mountains, a distance of 300 to 500 mi (480 to 800 km). It extends northward from the Mexican boundary far into Canada. Although the altitude of the plains increases gradually from 600 ft (180 m) or 1,200 ft (370 m) on the east to 4,000–5,000 ft (1,200–1,500 m) or 6,000 ft (1,800 m) near the mountains, the local relief is generally small. The semi-arid climate excludes tree growth and opens far-reaching views.^[9]

The plains are by no means a simple unit. They are of diverse structure and of various stages of erosional development. They are occasionally interrupted by buttes and escarpments. They are frequently broken by valleys. Yet on the whole, a broadly extended surface of moderate relief so often prevails that the name, Great Plains, for the region as a whole is well-deserved.^[9]

The western boundary of the plains is usually well-defined by the abrupt ascent of the mountains. The eastern boundary of the plains (in the United States) is more climatic than topographic. The line of 20 in (510 mm) of annual rainfall trends a little east of northward near the 97th meridian. If a boundary must be drawn where nature presents only a gradual transition, this rainfall line may be taken to divide the drier plains from the moister prairies.^[9] However, in Canada the eastern boundary of the plains is well defined by the presence of the Canadian Shield to the northeast.

The plains (within the United States) may be described in northern, intermediate, central and southern sections, in relation to certain peculiar features.^[9] In Canada, no such division is used: the climatic and vegetation regions are more impactful on human settlement than mere topography, and therefore the region is split into (from north to south), the taiga plains, boreal plains, aspen parkland, and prairie ecoregion regions.

Northern Great Plains

The Great Plains as seen in Minnesota's upland prairie at Glacial Lakes State Park

The northern section of the Great Plains, north of latitude 44°, includes eastern Montana, eastern Wyoming, most of North Dakota and South Dakota, southwestern Minnesota and portions of the Canadian provinces including southeastern Alberta, southern Saskatchewan and southwestern Manitoba. The strata here are Cretaceous or early Tertiary, lying nearly horizontal. The surface is shown to be a plain of degradation by a gradual ascent here and there to the crest of a ragged escarpment, the escarpment-remnant of a resistant stratum. There are also the occasional lava-capped mesas and dike formed ridges, surmounting the general level by 500 ft (150 m) or more and manifestly demonstrating the widespread erosion of the surrounding plains. All these reliefs are more plentiful towards the mountains in central Montana. The peneplain is no longer in the cycle of erosion that witnessed its production. It appears to have suffered a regional uplift or increase in elevation, for the upper Missouri River and its branches no longer flow on the surface of the plain, but in well graded, maturely opened valleys, several hundred feet below the general level. A significant exception to the rule of mature valleys occurs, however, in the case of the Missouri, the largest river, which is broken by several falls on hard sandstones about 50 mi (80 km) east of the mountains. This peculiar feature is explained as the result of displacement of the river from a better graded preglacial valley by the Pleistocene ice sheet. Here, the ice sheet overspread the plains from the moderately elevated Canadian highlands far on the north-east, instead of from the much higher mountains nearby on the west. The present altitude of the plains near the mountain base is 4,000 ft (1,200 m).^[9]

The northern plains are interrupted by several small mountain areas. The Black Hills, chiefly in western South Dakota, are the largest group. They rise like a large island from the sea, occupying an oval area of about 100 mi (160 km) north-south by 50 mi (80 km) east-west. At Black Elk Peak, they reach an altitude of 7,216 ft (2,199 m) and have an effe