The vaykay-spot-that-almost-was had a pretty bitching security system, thus locking the complex up tight following the nuclear holocaust that befell America. As time went on, the climate control and air conditioning system starting pushing toxins out into the nearby area, surrounding it with a mist of poison and making the adjoining city impossible to navigate. A small band of survivors, dubbed the Ghost People, have only managed to scrape by, seemingly resorting to capturing healthy people outside of the plume of pollution surrounding the Sierra Madre. You know, to eat them.
And that's pretty much all we have to go on right now. You can download "Dead Money" for Fallout: New Vegas on December 21, exclusively on Xbox Live, for 800 MS Points ($10).