Could it be something even more nefarious like a missile silo?
Living out here in Montana/Colorado/Wyoming/Nebraska area, we've been around the things since Day 1.
The link below shows an example (excuse the lack of a hot link please)
http://www.siloworld.net/576thSMS/PEACEKEEPER/LF-05/PK.HTM
Basically, they just look like a big concrete slab and if you wanted to waste your time (those intel satellites are supposed to spot the construction of missile silos) and cover 'em with something, you could get by with a lot less than that gaudy mess on Pedo Island.
That thing practically screams, "Hey, look at me!"
As far as being "nefarious", there have always been Urban Legends about tourists getting into those sites (most of 'em are within sight of secondary highways) and setting up camp or a picnic.
....until it's interrupted by a squad of heavily armed and irritated AF Security troops. #NoTheyAren'tKidding