The worst thing is, any area that doesn't have some sort of regular attention by an official agency will fall back into wrack and ruin through inattention. Even my favorite range requires an extra man and more time to clean up on Mondays, from junk left on the line. I've seen some very nice areas closed to shooting because of drunken slobs. Cars, refrigerators, water heaters, all kinds of garbage left out after being shot to ribbons, broken glass everywhere, spilled oil on the ground, it's sickening, and the major reason I won't shoot at wildcat ranges any more. I went to one that was so popular and overused that you literally couldn't take a step without stepping on discarded brass, shotgun hulls, broken glass or debris. The county sent in a bulldozer on that one, same day the area was chained off.
Start off by assuming whatever you do will get shot up. Any signs you post will get holes poked in them. Any benches will be shot, and target stands will get ruined or stolen. It is wort the effort if enough people get involved AND you can get local LE to run by once in a while to arrest slobs. See, none of the drunken bums will attend any of the meetings, even know there WAS a meeting, and will continue with what they do, littering and careless shooting, until the word gets out, hey, bad area, man, George and Jorge got arrested for endangerment and criminal littering last week, lets find somewhere else to get high and make noise!
BTW, best investment the group could make - rent a bulldozer and consult with an NRA range building officer - cut some REAL shooting lanes into the ground with real backstops. Signs need to be heavy duty metal, set way into the ground on torch resistant poles. If you build overheads, use thick wood, maybe even railroad ties. Anything light will be destroyed.
I've dealt with these type of people many times in the past, even knew some, and it always sickens me to see what they do to the landscape. Even worse when you point it out, and they have the me-first, blank stare of "What? I don't care!"
Last thing - do NOT confront slob shooters! Those who destroy the landscape for temporary fun may also be under the influence of recreational substances, and the last thing you want to do is confront someone who is under the influence, armed, with buddies. Be a good witness and call PD.