What are the Interior Plains?

The Interior Plains are the vast flat to gently rolling region of central Canada that lies between the Canadian Shield in the east and the Rocky Mountains in the west. The plains extend from the Beaufort Sea coast of the Northwest Territories south through the prairie provinces (Manitoba, Saskatchewan, and Alberta) to the United States border. They cover about 1.8 million square kilometres, more than 18 per cent of Canada's land area, and are the largest of Canada's seven physiographic regions after the Canadian Shield.

The Interior Plains are underlain by Mesozoic and Tertiary sedimentary rock (sandstone, shale, limestone, and coal seams) deposited between about 250 million and 35 million years ago, when most of the region was covered by the Western Interior Seaway. Pleistocene continental glaciers covered the entire region (except the Cypress Hills) up to about 12,000 years ago and left thick glacial till, outwash, and lacustrine sediment. The elevation generally rises from about 200 metres in southeastern Manitoba to 1,000 metres at the foothills of the Rockies, an imperceptible slope of about 30 centimetres per kilometre.

The Interior Plains have three sub-regions: the Manitoba Plain (elevations of 100 to 250 metres) in southern Manitoba and extreme southwestern Ontario, the Saskatchewan Plain (250 to 600 metres) covering most of Saskatchewan and southern Manitoba, and the Alberta Plateau (600 to 1,000 metres) covering most of southern and central Alberta plus parts of northeastern British Columbia. The Northern Interior Plains extend north into the Mackenzie River valley of the Northwest Territories.

The Interior Plains contain Canada's most productive agricultural land, with about 80 per cent of Canada's farmland. The Prairie Pothole Region of southern Saskatchewan and Manitoba is one of the world's most important waterfowl breeding areas. The Western Canadian Sedimentary Basin underlying the plains contains Canada's principal oil, natural gas, and coal reserves, including the Athabasca oil sands of northern Alberta (the third-largest oil reserves in the world after Venezuela and Saudi Arabia), the Montney and Duvernay shale gas plays, and the Bakken Formation in southeast Saskatchewan. Coal mining in the Crowsnest Pass and the Highvale mines in Alberta supports thermal-coal export to Asia. The plains support most of Canada's ranching industry, with Calgary, Edmonton, Saskatoon, Regina, and Winnipeg as the major agricultural service centres.