Teton (tētŏnˈ) [key]. 1 River, 143 mi (230 km) long, rising in several branches in the Rocky Mts., NW Mont., and flowing E to the Marias River. Bynum Reservoir, on a tributary, is a unit in the irrigation system of the Teton. 2 River, c.60 mi (100 km) long, rising in W Wyoming, in forks which unite in SE Idaho. The Teton flows N and W to Henrys Fork River, near Rexburg, Idaho. In its early course it runs through Teton Basin, formerly Pierre's Hole; a battle with the Gros Ventres Native Americans was fought (1832) there.