I-15 continues north onto the Snake River Plain and into the Fort Hall Indian Reservation. The highway accesses the reservation's main settlement, Fort Hall, via a diamond interchange with Ross Fork Road on the Bannock–Bingham county line. I-15 has a four-ramp partial cloverleaf interchange with US 91, at which the highway crosses over Union Pacific's Montana Subdivision rail line, near the northern edge of the reservation; I-15 Bus. splits northeast with US 91 from this interchange. The Interstate curves northeast and crosses the Blackfoot River and begins to parallel the Snake River as it passes along the western edge of the city of Blackfoot. I-15 Bus. reconnects with I-15 at a diamond interchange with US 26 (Bridge Street), which runs concurrently with the Interstate leaving Blackfoot. The highway crosses the Snake River at the northern edge of the city. I-15 has a partial cloverleaf interchange near Rose before it crosses a pair of irrigation canals. The Interstate then travels across the eastern part of the Hell's Half Acre Lava Field ahead of its interchange with River Road, which provides access to Shelley east of the Snake River.