The
Interior Plains is a vast physiographic region that spreads across the
Laurentian cratonLaurentia , like all craton land, was created as continents moved about the surface of the Earth, bumping into other continents and drifting away....
of North America. This area was originally formed when
cratonA 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 1.9–1.8 billion years ago in the
Trans-Hudson orogenyThe 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
PaleoproterozoicThe Paleoproterozoic is the first of the three sub-divisions of the Proterozoic occurring between . This is when the continents first stabilized...
.
Precambrian
metamorphicMetamorphic rock is the result of 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 rockIgneous rock is one of the three main rock types . Igneous rock is formed by magma being cooled and becoming solid. They may form with or without crystallization, either below the surface as intrusive rocks or on the surface as extrusive rocks...
s now form the basement of the Interior Plains and make up the stable nucleus of North America. With the exception of the
Black HillsThe Black Hills are a small, isolated mountain range rising from the Great Plains of North America in western South Dakota and extending into Wyoming, USA. Set off from the main body of the Rocky Mountains, the region is something of a geological anomaly—accurately described as an "island of trees...
of
South DakotaSouth Dakota is a state located in the Midwestern region of the United States of America. It is named after the Lakota and Dakota Sioux American Indian tribes. South Dakota was carved out of the southern half of the Dakota Territory and admitted to the Union on November 2, 1889...
, the entire region has low relief, reflecting more than 500 million years of relative
tectonicPlate tectonics is a theory which describes the large scale motions of Earth's lithosphere...
stability.
The Interior plains region of the
United StatesThe United States of America is a federal constitutional republic comprising fifty states and a federal district...
and
CanadaCanada is a country occupying most of northern North America, extending from the Atlantic Ocean in the east to the Pacific Ocean in the west and northward into the Arctic Ocean...
falls within this area.
The
Interior Plains is a vast physiographic region that spreads across the
Laurentian cratonLaurentia , like all craton land, was created as continents moved about the surface of the Earth, bumping into other continents and drifting away....
of North America. This area was originally formed when
cratonA 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 1.9–1.8 billion years ago in the
Trans-Hudson orogenyThe 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
PaleoproterozoicThe Paleoproterozoic is the first of the three sub-divisions of the Proterozoic occurring between . This is when the continents first stabilized...
.
Precambrian
metamorphicMetamorphic rock is the result of 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 rockIgneous rock is one of the three main rock types . Igneous rock is formed by magma being cooled and becoming solid. They may form with or without crystallization, either below the surface as intrusive rocks or on the surface as extrusive rocks...
s now form the basement of the Interior Plains and make up the stable nucleus of North America. With the exception of the
Black HillsThe Black Hills are a small, isolated mountain range rising from the Great Plains of North America in western South Dakota and extending into Wyoming, USA. Set off from the main body of the Rocky Mountains, the region is something of a geological anomaly—accurately described as an "island of trees...
of
South DakotaSouth Dakota is a state located in the Midwestern region of the United States of America. It is named after the Lakota and Dakota Sioux American Indian tribes. South Dakota was carved out of the southern half of the Dakota Territory and admitted to the Union on November 2, 1889...
, the entire region has low relief, reflecting more than 500 million years of relative
tectonicPlate tectonics is a theory which describes the large scale motions of Earth's lithosphere...
stability.
The Interior plains region of the
United StatesThe United States of America is a federal constitutional republic comprising fifty states and a federal district...
and
CanadaCanada is a country occupying most of northern North America, extending from the Atlantic Ocean in the east to the Pacific Ocean in the west and northward into the Arctic Ocean...
falls within this area. The Interior Plains were often covered by shallow
inland seasThe Western Interior Seaway, also called the Cretaceous Seaway, the Niobraran Sea, and the North American Inland Sea, was a huge inland sea that split the continent of North America into two halves during most of the mid and late Cretaceous Period.-Origin and geology:The Seaway was created as the...
.
SedimentSediment is any particulate matter that can be transported by fluid flow, and which eventually is deposited.Sediments are most often transported by water transported by wind and glaciers...
s from the shield and the
Rocky MountainsThe Rocky Mountains are a major mountain range in western North America. The Rocky Mountains stretch more than from the northernmost part of British Columbia, in Canada, to New Mexico, in the United States. The range's highest peak is Mount Elbert in Colorado at above sea level...
were deposited in these seas over millions of years. Eventually the sediments were compressed by the weight of the layers above into
sedimentary rockSedimentary rock is the type of rock that is formed by sedimentation of material at the Earth's surface and within bodies of water. Sedimentation is the collective name for processes that cause mineral and/or organic particles to settle and accumulate or minerals to precipitate from a solution....
. Part of the sedimentary rock deposited in these areas consists of
coral reefCoral reefs are aragonite structures produced by living organisms, found in marine waters containing few nutrients. In most reefs, the predominant organisms are stony corals, colonial cnidarians that secrete an exoskeleton of calcium carbonate...
s that formed close to the surface of seas during the
PaleozoicThe Paleozoic or Palaeozoic Era is the earliest of three geologic eras of the Phanerozoic eon...
era.
Geology and physiography
The Interior Plains are a vast
physiographic divisionThe physiographic regions of the world are a means of defining the Earth's landforms into distinct regions based upon Nevin Fenneman's classic three-tiered approach of divisions, provinces and sections, in 1916, which although they date from the mid 1910s, are still considered basically valid, and...
encompassing 8 distinct physiographic provinces, the Interior Low Plateaus,
Great PlainsThe Great Plains are the broad expanse of prairie and steppe which lie 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 DeltaThe Mackenzie River originates in Great Slave Lake, in the Northwest Territories, and flows north into the Arctic Ocean. It is the longest river in Canada at and, together with its headstreams the Peace and the Finlay, the second longest river in North America at in length. The Mackenzie and...
, Manitoba Lowlands, Northern Boreal Plains, Prairie Grasslands, and the Southern Boreal Plains And Plateaux.
Paleozoic and Mesozoic
Throughout the
PaleozoicThe Paleozoic or Palaeozoic Era is the earliest of three geologic eras of the Phanerozoic eon...
and
MesozoicThe Mesozoic Era is one of three geologic eras of the Phanerozoic eon. The division of time into eras dates back to Giovanni Arduino, in the 18th century, although his original name for the era now called the "Mesozoic" was "Secondary" The Mesozoic Era is one of three geologic eras of the...
eras, the mostly low-lying Interior Plains region remained relatively unaffected by the
mountain-buildingOrogeny refers to natural mountain building, and may be studied as a tectonic structural event, as a geographical event, and a chronological event...
tectonic collisions occurring on the western and eastern margins of the continent. During much of the Mesozoic Era, the North American continental interior were mostly well above sea level, with two major exceptions. During part of the
JurassicThe Jurassic is a geologic period and system that extends from about Ma to Ma, that is, from the end of the Triassic to the beginning of the Cretaceous. The Jurassic constitutes the middle period of the Mesozoic era, also known as the "Age of Reptiles". The start of the period is marked by...
, rising seas flooded the low-lying areas of the continent, forming the
Sundance SeaThe Sundance Sea was an epeiric sea that existed in North America during the mid to late Jurassic Period of the Mesozoic Era. It was an arm of what is now the Arctic Ocean, and extended through what is now western Canada into the central western United States...
; in the
CretaceousThe Cretaceous , Latin language for "chalky", usually abbreviated K for its German translation Kreide , is a geologic period and system from circa to million years ago . In the geologic timescale, the Cretaceous follows on the Jurassic period and is followed by the Paleogene period of the...
, much of the Interior Plains region lay submerged beneath the
Western Interior SeawayThe Western Interior Seaway, also called the Cretaceous Seaway, the Niobraran Sea, and the North American Inland Sea, was a huge inland sea that split the continent of North America into two halves during most of the mid and late Cretaceous Period.-Origin and geology:The Seaway was created as the...
.
Cenozoic
The Interior Plains continued to receive deposits from the eroding
Rocky MountainsThe Rocky Mountains are a major mountain range in western North America. The Rocky Mountains stretch more than from the northernmost part of British Columbia, in Canada, to New Mexico, in the United States. The range's highest peak is Mount Elbert in Colorado at above sea level...
to the west and
AppalachianThe Appalachian Mountains , often called the Appalachians, are a vast system of mountains in eastern North America. Definitions vary on the precise boundaries of the Appalachians...
and Ozark/
Ouachita MountainsThe Ouachita Mountains are a mountain range located in west central Arkansas, southeastern Oklahoma and north-east Texas. The range's subterranean roots may extend as far as central Texas, or beyond it to the current location of the Marathon Uplift...
to the east and south throughout the era. The flatness of the Interior Plains is a reflection of the platform of mostly flat-lying marine and stream deposits laid down in the Mesozoic and Cenozoic eras.