Hebgen Dam is a concrete-core earthen embankment dam on the Madison River in the U.S. state of Montana . The dam is 85 feet tall and 721 feet long . The dam 's purpose is to store and regulate water for other downstream reservoirs and hydroelectric power plants . Montana Power Company originally built the dam , PPL Corporation purchased it in 1997 and sold it to NorthWestern Corporation in 2014 . Hebgen Dam was built across the Madison River in 1914 by Montana Power Company to create Hebgen Lake . During the 7.5 magnitude 1959 Hebgen Lake earthquake , the dam was damaged , primarily because of such intense ground movement that water surged over the dam crest four different times , but it was fixed several weeks later . The epicenter of the quake was determined to be beneath the bottom of Hebgen Lake . Seismologists reported it to be the fourth largest quake recorded in the United States up to that time . On August 30 , 2008 , two of the dam 's four hydraulic gates failed , releasing per second of water into the Madison River . The normal discharge of the dam is per second and the gate failure caused a 1-foot rise in the river
1959 Hebgen Lake earthquake
1959 Hebgen Lake earthquake
Hebgen Dam