The U.S. Army's Sioux Ordnance Depot was established in western Nebraska on March 23, 1942. It was the only Army ammunition depot in Nebraska during WWII, the Korean War and the Vietnam War.

U.S. Army munitions were housed in 801 lumps of earth largely invisible from the skies, but dotting the ground like igloos over an area of 19,771 acres.

The depot was decommissioned on June 30, 1967.  Now unused by the military, many of these "igloos" have turned into storage facilities and garages for farmers who use them for their equipment and supplies.