The Interior Plains is a vast physiographic region that spreads across the Laurentian craton

Laurentia

Laurentia is a large area of continental craton, which forms the ancient geological core of the North American continent...

 of central North America

North America

North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...

.
The Interior Plains are an extensive physiographic division

Physiographic regions of the world

The physiographic regions of the world are a means of defining the Earth's landforms into distinct regions based upon classic 1916 three-tiered approach defining divisions, provinces, and sections...

 encompassing 8 distinct physiographic provinces, the Interior Low Plateaus, Great Plains

Great Plains

The Great Plains are a broad expanse of flat land, much of it covered in prairie, steppe and grassland, which lies west of the Mississippi River and east of the Rocky Mountains in the United States and Canada. This area covers parts of the U.S...

, Central Lowland, Mackenzie Delta

Mackenzie River

The Mackenzie River is the largest river system in Canada. It flows through a vast, isolated region of forest and tundra entirely within the country's Northwest Territories, although its many tributaries reach into four other Canadian provinces and territories...

, Manitoba Lowlands, Northern Boreal Plains, Prairie Grassland and the Southern Boreal Plains and Plateaux'.
This area was originally formed when craton

Craton

A craton is an old and stable part of the continental lithosphere. Having often survived cycles of merging and rifting of continents, cratons are generally found in the interiors of tectonic plates. They are characteristically composed of ancient crystalline basement rock, which may be covered by...

s collided and welded together 1.8–1.9 billion years ago in the Trans-Hudson orogeny

Trans-Hudson orogeny

The Trans-Hudson orogeny, Trans-Hudsonian orogeny, Trans-Hudson orogen , or Trans-Hudson Orogen Transect , , was the major mountain building event that formed the Precambrian Canadian Shield, the North American craton , and the...

 during the Paleoproterozoic

Paleoproterozoic

The Paleoproterozoic is the first of the three sub-divisions of the Proterozoic occurring between . This is when the continents first stabilized...

 Era.

Precambrian metamorphic

Metamorphic rock

Metamorphic rock is the transformation of an existing rock type, the protolith, in a process called metamorphism, which means "change in form". The protolith is subjected to heat and pressure causing profound physical and/or chemical change...

 and igneous rock

Igneous rock

Igneous rock is one of the three main rock types, the others being sedimentary and metamorphic rock. Igneous rock is formed through the cooling and solidification of magma or lava...

s now form the basement of the Interior Plains and make up the stable nucleus of North America.