Flood Zones in Madison County, Idaho

June 5, 1976: a brand-new dam failed and much of the county flooded within hours

Teton Dam, a 305-foot earthen dam across the Teton River on the Madison-Fremont county line, catastrophically failed on June 5, 1976 -- just months after it was completed. The resulting flood killed 11 people, caused an estimated $400 million in damages (in 1976 dollars), and ravaged roughly 190,000 acres of agricultural land across the region. A roughly 15-foot wall of water reached Wilford and Sugar City, both inside Madison County, and struck Rexburg not long after; within minutes, an estimated 80 percent of Rexburg itself was inundated to depths of six to eight feet. The flood ultimately traveled some 93 miles down the Teton River before it was retained at American Falls Reservoir, and the U.S. Geological Survey later produced a detailed hydrologic atlas of the flood's extent, covering the area from the dam site downstream, including the Rexburg quadrangle.

The dam was never rebuilt, and the river still flows unchecked through the breach

Teton Dam has never been rebuilt. The failure site remains publicly accessible today, and more importantly for a land buyer, the Teton River drainage flows through the old dam site unchecked by any impoundment -- reporting around the flood's fiftieth anniversary describes this unregulated flow as causing real, ongoing damage in wet years, rather than the failure being a one-time historical event with no present-day consequence. There has also been an active, organized push in recent years -- including advocacy from state legislators -- to study or pursue rebuilding the dam, on the argument that modern dam engineering has advanced substantially since 1976; that effort remains a live, unresolved policy question as of this research pass, not a settled plan, and its outcome either way would materially change the flood-risk and land-use picture along the Teton River corridor in Madison County.

For a buyer evaluating land along the Teton River corridor in Madison County -- including the Sugar City, Salem, and Hibbard areas, and land near Rexburg's river frontage -- this history is directly relevant, not just a historical curiosity: an unregulated river channel through a documented former dam-failure zone is a different risk profile than a river with an upstream flood-control structure. Confirm the specific FEMA Flood Insurance Rate Map (FIRM) zone designation for any specific parcel directly through FEMA's Map Service Center or Madison County's own floodplain administration before assuming a parcel's flood risk based on distance from the river alone; this page did not independently verify current, parcel-level FIRM boundaries.