I would avoid wheeling around the Mirage I hear that the security there is a real tiger....In all seriousness check out www.4x4trails.net forget about that I just checked and there is nothing...MOAB is probably 7-8 hours away. Farmington, NM probably 5-6 hours away, or you could go towards the freaky state of Cali~forn~i~a (in my best Arnold voice)
There used to be some good wheeling up toward Pahrump, Nevada but I haven't been there since they put new casinos in so I don't know how populated the place is now. There's no real legal place. Just point your truck down a dirt road and explore.