Designation of Missouri River segment as a wild and scenic river : hearing before the Subcommittee on National Parks and Recreation of the Committee on Interior and Insular Affairs, House of Representatives ; Ninety-fourth Congress, second session ; on S. 1506, to designate a segment of the Missouri River, Montana, as a component of the Naitonal Wild and Scenic Rivers System ; hearing held in Washington, D.C. ; June 21, 1976