Little Missouri. 1 River, c.145 mi (230 km) long, rising in the Ouachita Mts., SW Ark., and flowing generally SE to join the Ouachita River N of Camden. North of Murfreesboro is Narrows Dam (1950), which impounds Lake Greeson. 2 River, c.560 mi (900 km) long, rising in NE Wyo. and flowing NE into Garrison Reservoir on the Missouri River, W N.Dak. It flows through Theodore Roosevelt National Memorial Park.