The claim: Birthplace of the infamous "Would you shoot American citizens?" Quiz. New camps being built on "back 40".
What it really is: First, the actually name of the base is the "Marine Corps Air Ground Combat Center Twentynine Palms" and is located right inside the Morongo Basin and the High Desert region of the Mojave Desert.
Using Google maps I've taken a look at the base and the area around it, and while there are some small buildings around the main part of the base itself, none of them are large enough to hold large amounts of people, nor do most of them even appear to be fenced in.
As for the "Would you shoot American citizens?" quiz, it's still questionable if this was even real, but from what information from I can find (mind you this is from conspiracy theorists, so it might all be a hoax) it was apparently part of a marine survey (and not an actual quiz) done back in the mid 1990's, and according to the claims that I found, the overwhelming majority of them said that they wouldn't.