Beaverhead River

The Beaverhead River is an approximately 69-mile-long (111 km) tributary of the Jefferson River in southwest Montana (east of the Continental Divide). It drains an area of roughly 4,778 square miles (12,370 km). The river's original headwaters, formed by the confluence of the Red Rock River and Horse Prairie Creek, are now flooded under Clark Canyon Reservoir, which also floods the first 6 miles (9.7 km) of the river. The Beaverhead then flows through a broad valley northward to join the Big Hole River and form the Jefferson River. With the Red Rock River included in its length, the river stretches another 70 miles (110 km), for a total length of 139 miles (224 km), one of the more significant drainages of south-western Montana.