Slab city is a closed military base. When the military moved out they tore down the buildings leaving a bunch of concrete slabs, I'ts boondocking. A lot of the folks who camp there are, from what I understand, from the low end of the RV barrell, which is not to say some nice rigs don't park there from time to time. No authority governs it and I gather is a bit "wild" (As in bad lands)
i have found alot of info on the net and none of it talks about crime, some of the comments seem to talk about the class of people but no one talks about having any trouble when staying there. i would much prefere old trailers and friendly people than a high crime area as soon as you leave the campground you are in, or a place where everone is waiting to see what you do wrong or what they can complain about.
Slab City is just northeast of Niland, CA on the east side of the Salton Sea. Take State Hwy 111 to Niland, then follow "Main Street" out of town and a couple of miles past the railroad tracks. I don't remember the name of the military base - it was set up for WWII and dismantled at the end of the war leaving nothing but the roads and slab building foundations. Since the mid-60s it's been a self-governing community with minimum interference from the county government.
I've enjoyed my visits there. During the winter you'll find all kinds of people. Everything from the "slobs" as Terry puts it (people with minimum income who are pretty much stuck there) to more affluent fulltimers taking a break from the road. During the summer months you'll find mostly permanent or semi-permanent residents. Several RV groups like Loners on Wheels have semi-permanent encampments set up.
Like any other community, Slab City has it's good points and bad. If you go in and throw your weight around you'll probably have a bad experience. Try and blend in with the existing community and you'll probably have a good time.
If you don't like what you see when you arrive, there are several commercial hot spring RV resorts and a state park a little further north on Highway 111.
Unfortunately, the "official" web site will make you send in a $5 "donation" before letting you see any of the inside pages. I suggest doing a Google search first. "Slab City" will turn up hundreds of articles.
Not all of the links require the "donation", you can read the bulletin board and read the events calendar. But, yes, a 10 second search on Google will turn up lots of other information, more than we could ever give here.