It is located in the middle of nowhere in Nevada. It is a "secret" test facility that in the past is where they tested (secretly, sort of) the U-2, SR-71, F-117, B-2 and others. Who knows if they are still testing there or not. It is also where the military keeps all the alien spacecraft that they are reverse engineering, in Hanger 18.

(see Urban Legends)
There are so many rumors about this place that who knows what is true. But they do have some of the most sophisticated alarm systems in the country.
At one time there was a hill about 12 miles away that people would use telescopes to watch the base, but the govmt was suddenly the owner and it was closed to everyone. I'm sure all countries have secret testing areas, ours is just the most famous secret (oxymoron?) base.
Vern.