The Physical Geography of the Great Plains

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University of the Philippines Diliman
College of Social Sciences and Philosophy
Department of Geography

Final Paper in Geography 155
THE GREAT CENTRAL PLAINS

Mary Angelie A. Pasion

PHYSICAL BACKGROUND OF THE GREAT CENTRAL PLAINS

General Information and Physical Background
The North American Plains include the area from the Canadian boreal forest in the north to central Texas in the south and from the Rocky Mountain in the west to the Missouri River and the eastern boundaries of the states of Nebraska, Kansas, and Oklahoma in the east. This region is almost continuous open grassland, interrupted by more forested locales along the major river valleys and in those areas, such as the Black Hills of eastern Wyoming and western South Dakota, where the expanse of open plains was interrupted by isolated mountainous areas. Located at 40° 19' N; 99° 25' W, Great Central Plains’ is a geographically-defined sub-range with Bald Mountain (7881 ft/2402 m) as its highest point. The area it covers that includes the lowland areas is 225,440 sq. mi/ 583,890 sq.km. It extends 631 mi from the North to South and 774 mi from the East to west. It covers 34% of Nebraska, 29% of Kansas, 13% of Colorado, 8% of South Dakota, 8% of Wyoming, 5% of Missouri and 3% of Oklahoma.

Climate
The Plains climate is extremely unpredictable, but is generally characterized by summer-dominant rainfall. There is a steep east to west decrease in precipitation, and cold winters. In general, it has a wide variety of weather throughout the year, with very cold winters and very hot summers. Wind speeds are often high. 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 20 inches (510 millimetres) or more of rainfall per year and an area that receives less than 20 in (510 mm). 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.

The Geologic Story of Great Plains
The Interior Plains, of which the Great Plains is the western, mostly not glaciated, is the least complicated part of the continent geologically except for the Coastal Plain. For most of the half billion years from 570 million until about 70 million years ago, shallow seas lay across the interior of our continent. A thick sequence of layered sediments, mostly between 5,000 and 10,000 feet thick, but more in places, was deposited onto the subsiding floor of the interior ocean. These sediments, now consolidated into rock, rest on a floor of very old rocks that are much like the ancient rocks of the Superior Upland. About 70 million years ago the seas were displaced from the continental interior by slow uplift of the continent, and the landscape that appeared was simply the extensive, nearly flat floor of the former sea. During warping and stream deposition, most of these rocks of marine origin lie at considerable depth beneath the land surface, concealed by an overlying thick, layered sequence of rocks laid down by streams, wind, and glaciers. Nevertheless, their geologic character, position, and form are exceptionally well known from information gained from thousands of wells that have been drilled for oil. The initial, nearly...