Interior Plains
[1] A series of tectonic plate collisions in the crust that formed the center of the North American continent laid the groundwork for the modern-day interior plains.
The interior of Laurentia remained relatively flat and became a basin for eroded sediment from mountains at the beginning of the current time period, the Phanerozoic Eon.
The sediments that formed the Black Hills were granite and different types of igneous rocks, which make up the basement of bedrock in central North America.
When global sea level rose and continents became partially submerged, the oceans had an explosion of complex life, which was the first time an event like this occurred on Earth.
However, the center of Laurentia remained above sea level and as the continent moved east towards other supercontinents like Gondwana, the Appalachian Mountains began to form around 400 MYA.
Sediments deposited in the interior plains from this era are currently buried deep beneath the surface where they are difficult to study.
This body of water extended from present-day Alaska to the Gulf of Mexico and covered almost all the interior plains west of the current boundary of the Mississippi River.
The outcrops seen at the surface of the Rockies are made up of sandstone, granite, and limestone; as well as metamorphic rocks uplifted from the Proterozoic Period.
In glaciated conditions, sand and silt-laden meltwater originating from alpine glaciers in the Rocky Mountains generated alluvial deposits at their base.
That loess is so prevalent in the Interior Plains is evidence of significant aeolian erosion, as deposits are generally accumulations of wind-blown dust.
In the years following the Dust Bowl, 18,500 miles (29,800 km) of shelterbelt were planted by the Works Progress Administration to reduce wind intensity.
Prairies on the eastern side of the Interior Plains are dominated by tall grass varieties including big bluestem and switchgrass.
[28] Other significant crops produced in the region include barley, corn, cotton, sorghum, soybeans, and canola, which is particularly important to Canadian exports.
[26] The Interior Plains physiographic area stretches across Canada and the United States, and the two governments each use a different hierarchical system to classify their portions.
In Canada, the Interior Plains makes up one of seven physiographic areas included in the highest level of classification - defined as a "region" in that country.
For other physiographic regions (such as the Interior Plains and Appalachian Uplands) subregions are not developed, but the tertiary level (called "division" in Canada) is used in the mapping data.
Further information can be found at https://atlas.gc.ca/phys/en/index.html The following is a breakdown of the secondary (provinces), and tertiary (sections) physiographic areas of the Interior Plains portion in the United States:[32]
