<P> The Powder River Basin is a geologic structural basin in southeast Montana and northeast Wyoming, about 120 miles (190 km) east to west and 200 miles (320 km) north to south, known for its coal deposits . The region supplies about 40 percent of coal in the United States . It is both a topographic drainage and geologic structural basin . The basin is so named because it is drained by the Powder River, although it is also drained in part by the Cheyenne River, Tongue River, Bighorn River, Little Missouri River, Platte River, and their tributaries . </P> <P> While the Powder River Basin is unified geologically, residents of areas distant from the Powder River proper do not think of themselves as living in a single geographic region . For example, residents of the Crow Reservation in the Big Horn River watershed, or of Sheridan in the Tongue River watershed, would locate the Powder River Basin as the region east of the Big Horn Mountains, using a definition based on watershed and topography . </P>

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