The Coos River flows for about 5.5 miles (8.9 km) into Coos Bay along the Pacific coast of southwest Oregon in the United States. Formed by the confluence of its major tributaries, the South Fork Coos River and the Millicoma River, it drains an important timber-producing region of the Southern Oregon Coast Range. The course of the Coos River and its major tributaries is generally westward through the mountains to the short main stem, which flows into the eastern end of Coos Bay near the city of Coos Bay.