Interior Plains

The Interior Plains are a great physio geographic region of the supercontinent Laurentia in North America today. They originated as cratons before 1.8 to 1.9 million years collided in the Trans -Hudson orogeny during the Paläoproterozoikums. This metamorphic and igneous rocks form the base. In addition to the Black Hills in South Dakota, the area is relatively flat. In the past, this region was the Western Interior Seaway covered in the sediments from the Rocky Mountains deposed millions of years. They were forced through the overlying layers to sedimentary rocks. Of these, some made to coral reefs that have shaped the seafloor during the Palaeozoic.

Geology

The Interior Plains have as large physiographic region eight different provinces:

• Central Lowland
• Great Plains
• Interior Low Plateau
• Mackenzie Delta
• Manitoba Lowlands
• Northern Boreal Plains
• Prairie Grasslands
• Southern Boreal Plains and Plateaus

Paleo-, Meso - and Cenozoic

From the orogeny in the Paleo- Mesozoic and the region remained unaffected. Except in the Jurassic, when there was the Sundance Sea, and in the Cretaceous when there was the Western Interior Seaway, the region was above sea level.

In Cenozoic sediments from the erosion of the Rocky Mountains and the Appalachian Mountains, the Ouachita Mountains and the Ozark Plateau were deposited. That is reason for making sure the area is relatively flat.

• Physical Geography