By far the most submitted link is to the notorious Area 51. Props go to Andy who was the first of many to point us in the right direction, cheers mate Travis added:

Scroll to the south-west and find that pock-marked stretch of desert. That’s where our government tested nuclear weapons.

Edwards Air Force Base has this giant compass-thing scraped into the desert. I assume it’s to help pilots orientate themselves when landing or taking off.