Powder River

River in the northeast of Wyoming and the southeast of Montana, named after the black sand along its banks that resembles gunpowder; length 781 km/485 mi. In its upper reaches, the river valley is extremely rich in bituminous coal.

The Powder River rises from several forks in the foothills of the Bighorn Mountains of Wyoming, and flows north through sparsely populated cattle- and sheep-ranching country before crossing into Montana. It then continues roughly northeast to join the Yellowstone River just south of Terry. The Powder River's main tributaries are the Little Powder River in Wyoming and Montana and Crazy Woman Creek in Wyoming.