If you have specific National Forests or BLM districts go to their website and they will show all their CG. Freecampsites is very good. Or just a good paper map and look for the little green tree symbols that a lot of them use for campsites. I don't have it but a lot seem to like the Allstays app, I think it costs $9. You basically have to do your own research. CG near a city are asking for trouble. In my many years of camping I saw a situation like what you describe once, and it turned out to be a camp out of the Rainbow Tribe (may be extinct now) a mob of wandering hippies and bums. But we do not camp near any large cities.