When completed in 1918 by the Montana Power Company and the United Missouri River Power Company, its reservoir flooded the Gates of the Mountains, a limestone canyon which Meriwether Lewis described as "the most remarkable clifts that we have yet seen ... the towing and projecting rocks in many places seem ready to tumble on us."
Cando foi completada en 1918 pola Montana Power Company e a United Missouri River Power Company, o seu encoro alagou as Gates of the Mountains, un canón de pedra calcaria que Meriwether Lewis describiu como «os cantiis máis salientables que se virón... os torreóns e as rochas que sobresaen en moitos lugares parecen dispostos a caer sobre nós».