I was born and raised in western South Dakota. As a child, we would take weekend drives through the Black Hills and farther south, to Hot Springs/Edgemont area.
We drove out to and around Igloo, SD many times just because it was sooooo desolate and creepy. And Dad was chomping at the bit to get on the installation with his metal detector. But it's big, spread out and was nearly dissolved into the dust even 30 years ago. Everything above ground was desolate and deserted. But at that time, they were taking the nuke missiles out of all the silos in that area. There were hundreds of the nuclear missile silo sites out in the wide open ranch land. I had a friend who bought one in the 80s and made a home/bunker out of it. Ran fiber optic lines from the top to bring sunlight to the bottom. He was very techno-inclined.
Igloo had mutant sheep, cattle born in the area in the 60s and 70s.