I believe there may have been a post war settlement there, a group of people who moved those cars into walls and set up those barries. There is no way that Arkansas did that and I doubt raiders would spend there time building that just to let an old man walk in with a sniper rifle and scare them away.
And then there is the matter of the mines, why are they there? I think that maybe when those people abandon that settlement (if they did infact leave) they didn't want people (or raiders) to go or live there. Another possibility is raiders wiped out the settlement, found or had a lot of landmines and placed them all over the place, so the settlementwouldn't be recolonized for many years.