View of the Great Plains near Lincoln, Nebraska
The Great Plains are the broad expanse of prairie, steppe and grassland 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. states of Colorado, Kansas, Montana, Nebraska, New Mexico, North Dakota, Oklahoma, South Dakota, Texas, and Wyoming, and the Canadian provinces of Alberta, Manitoba and Saskatchewan. Some geographers include some territory of Mexico in the Plains, but many stop at the Rio Grande. In Canada the term prairie is more common, and the region is known as the Prairie Provinces or simply "the Prairies."
The region is about east to west and north to south. Much of the region was home to American Bison herds until they were hunted to near extinction during the mid/late 19th century. It has an area of approximately . Current thinking regarding the geographic boundaries of the Great Plains is shown by this map at the Center for Great Plains Studies, University of Nebraska–Lincoln.
The term "Great Plains", for the region west of about the 96th or 98th meridian and east of the Rocky Mountains, was not generally used before the early 20th century. Nevin Fenneman's 1916 study, Physiographic Subdivision of the United States, brought the term Great Plains into more widespread usage. Before that the region was almost invariably called the High Plains, in contrast to the lower Prairie Plains of the Midwestern states. Today the term "High Plains" is used for a subregion of the Great Plains.
The Great Plains are the westernmost portion of the vast North American Interior Plains, which extend east to the Appalachian Plateau. The United States Geological Survey divides the Great Plains in the United States into ten physiographic subdivisions:
The High Plains is used in a related, more general context to describe the elevated regions of the Great Plains, which are primarily west of the 100th meridian in the US.
During the Cretaceous Period (145-65 million years ago), the Great Plains was covered by a shallow inland sea called the Western Interior Seaway. However, during the Late Cretaceous to the Paleocene (65-55 million years ago), the seaway had begun to recede, leaving behind thick marine deposits and a relatively flat terrain where the seaway had once occupied.
Paleontological finds in the area have yielded bones of woolly mammoths, saber toothed tigers and other ancient animals, as well as dozens of other megafauna (large animals over ) – such as giant sloths, horses, mastodons, and American lion – that dominated the area of the ancient Great Plains for millions of years. The vast majority of these animals went extinct in North America around 13,000 years ago during the end of the Pleistocene.
In general, the Great Plains have a wide variety of weather throughout the year, with very cold winters and very hot summers. Wind speeds are often high. The prairies support abundant wildlife in undisturbed settings. Humans have converted much of the prairies for agricultural purposes or pastures.
The 100th meridian roughly corresponds with the line that divides the Great Plains into an area that receive or more of rainfall per year and an area that receives less than . In this context, the High Plains, as well as Southern Alberta, south-western Saskatchewan and Eastern Montana are mainly semi-arid steppe land and are generally characterised by rangeland or marginal farmland. The region (especially the High Plains) is periodically subjected to extended periods of drought; high winds in the region may then generate devastating dust storms. The eastern Great Plains near the eastern boundary falls in the humid subtropical climate zone in the southern areas, and the northern and central areas fall in the humid continental climate.