Powder River Basin
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The Powder River Basin is both a a topographic drainage and geologic structural basin. The region covers southeast Montana and northeast Wyoming and is about 120 miles east to west and 200 miles north to south. The basin is so named because it is drained by the Powder River. It is the single largest source of coal mined in the United States, and contains one of the largest deposits of coal in the world. Major cities in the area include Gillette and Sheridan, Wyoming and Miles City, Montana. The area is very sparsely populated and is known for its rolling grasslands and semiarid climate.
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[edit] Coal
The low sulfur and ash content of the coal in the region makes it very desirable. Much of the output of the basin's mines is used to fire power plants, east of the Rocky Mountains for generating electricity. In recent years over 350 million tons of coal have been mined annually, more than 25% of the total U.S. production. More than eighty train loads of coal, which vary in size from 125 to 150 cars, are shipped from Wyoming mines each day.
It has been estimated that Powder River Basin coal deposits contain over 800 billion tons of coal. The thickness of the coal seams in the region ranges up to 200 feet (60 m) and averages nearly 80 feet.
[edit] Coalbed Methane
Recent controversy surrounds the extensive coalbed methane extraction in the region. In the last decade, nearly 7000 of these wells have been drilled. Extracting the gas requires water to be pumped to the surface in order to release the gas trapped in the coal seam. While most of the water is successfully utilized in agriculture production such as livestock water and crop irrigation, some waters are naturally high in salinity. There has been controversy on how to best manage these saline waters.
[edit] Petroleum
The Powder River Basin also contains major deposits of petroleum.
The region also contains major deposits of uranium, contained in sandstones.
[edit] Geologic History
The coal beds of the region began to form about 60 million years ago when the land began rising from a shallow sea. When the coal beds were forming the climate in the area was subtropical, averaging about 120 inches of rainfall a year. For some 25 million years, the basin floor was covered with lakes and swamps. Because of large area of the swamps, the organic material accumulated into peat bogs instead of being washed to the sea. Periodically the layers of peat were covered with sediments washed in from nearby mountains. Eventually the climate became drier and cooler. The basin filled with sediment and buried the peat under thousands of feet, compressing the layers of peat and forming coal. Over the last several million years, much of the overlying sediment has eroded away, leaving the coal seams near the surface.
[edit] Power Plants fueled from Basin
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