 the beaverhead river is an approximately  tributary of the jefferson river in southwest montana (east of the continental divide). it drains an area of roughly . 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  of the river.{{cite web |url=http://fwp.mt.gov/fishing/guide/q_beaverhead_river__1123386455677.aspx |title=beaverhead river |publisher=montana fishing guide |date=
Landforms_of_Beaverhead_County,_Montana Landforms_of_Madison_County,_Montana Rivers_of_Montana