river, in the western United States, rising in the White River National Forest of northwestern Colorado, in the Rocky Mountains. Draining an area of approximately 9,500 square miles (24,600 square km) in south-central Wyoming and northwestern Colorado, the river flows north past Steamboat Springs, then turns west to flow through Yampa Canyon (about 1,600 feet 【490 metres】 deep) in Dinosaur National Monument and joins the Green River near the Utah border after a course of about 250 miles (400 km). Its chief tributary, the Little Snake, joins it from the north immediately east of the monument. The river's name probably derives from an Indian group.