Borderlands: Interior Plains Physiographic Region

The physical geography of Canada comprises two great parts: the Shield and the Borderlands. The Shield consists of a core of old, massive, Precambrian crystalline rocks. The Borderlands areas are formed by younger rocks and surround the Shield like two rings. The inner ring comprises a chain of lowlands, plains and plateaus of generally flat-lying sedimentary rocks. The outer ring consists of discontinuous areas of mountains and plateaus in which the younger rocks are deformed. Each of these areas is divided into regions, each of which comprises many smaller subdivisions that are distinctive based on their topography and geology.

Interior Plains Physiographic Region

The Interior Plains occupy the region between the Shield on the east and the mountains of the Cordilleran Region on the west. They join with the St. Lawrence Lowlands of eastern Canada through the United States and are separated from the Arctic Lowlands by the Amundsen Gulf. The southern part is characterized by semi-arid prairie, the central part is tree covered and the northern part is covered by the tundra. The region is divided into several subdivisions, those in the north being smaller and more varied than those in the south.

In the north, the Horton and Anderson Plains form the Arctic slope. The Peel Plain, which lies southwest of the Mackenzie River, forms a broad, shallow hollow in which some areas have innumerable small lakes and others have none.

West of the Peel Plain, the Peel Plateau rises in steps between the Peel Plain and the Mackenzie Mountains. On the east, the Colville Hills embrace several ridges that stand above the general level of the surrounding plains. Located around Great Bear Lake, the Great Bear Plain has a rolling surface. In contrast, the Great Slave Plain has generally little relief.

Located in the centre of the Interior Plains, the Alberta Plateau consists of a ring of plateaus separated by wide valleys. The two main valleys (Fort Nelson and Peace River lowlands) occupy more than 50 per cent of the area. These two rivers and their main tributaries are more or less entrenched into the valleys.

South of the Athabasca River, the Alberta Plain stretches southeastward to the Canada–United States boundary. Although a continuation of the Alberta Plateau, it has a more even surface, with a few widely separated groups of low hills, such as Cypress Hills in the south. The Cypress Hills reach an elevation of more than 1400 metres.

The eastern edge of the Alberta Plain forms a step down to Saskatchewan Plain, which is lower and smoother than the Alberta Plain. On the east, the Saskatchewan Plain is bordered by the Manitoba Escarpment, overlooking the Manitoba Plain. Streams flowing eastward have deep cut valleys, which divide the Manitoba Plain into a line of separate hills. The Manitoba Plain is largely covered by lakes and includes most of Lake Winnipeg.

The following photographs show examples of landscapes from the Interior Plains.

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Athabasca River, Alberta

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Peace River, British Columbia

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Valley of Battle Creek, Saskatchewan

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Qu' Appelle Valley, Saskatchewan

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Red River, Manitoba

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