During the Cold War, parts of South Dakota, Wyoming, Montana, and Colorado concealed hundreds of Minuteman II missiles scattered across ranch and prairie grasslands, including nearly a dozen sites visible from Interstate 90 in western South Dakota along routes to Mount Rushmore National Memorial and Yellowstone National Park. These weapons on the Great Plains were considered important to the safety of the United States, while each missile carried the potential for unimaginable destruction. Installed there for more than 30 years, they served to deter nuclear threats from the Soviet Union.