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Powder River BasinThe Powder River Basin spanning the Montana - Wyoming border is the single largest source of coal mined in the United States. The region contains one of the largest deposits of coal in the world. 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. Major cities in the area are Gillette and Sheridan, Wyoming and Miles City, Montana. This area of the U.S. is very sparsely populated and is rolling grasslands with an arid climate. 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 plants in the Midwest, such as Jeffrey Energy Center, 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. Over eighty 110 car trainloads of coal 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 (60m) and averages nearly 80 feet. Recent controversy surround proposals for the development of methane gas wells in the region. In the last decade nearly 7000 of these wells have been drilled. Extracting the gas involves methods that have negative environmental impact, particularly water pollution. Geological 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 a 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. The region also contains major deposits of uranium. External Links
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