The prob with this is that not only ATVers are in cause. Only A-HOLES. Everywhere I have been and seen closed riding areas...it didn't make a lot of a difference about trash and dumped cars. It even got worse sometimes.
Where I ride, i's already forbidden (but cops don't say nothing about it), and there are 3 rusted burnt cars on a 10 mile long section. If I had a truck big enough to pull them out of there, I would probably do it...but my poor Ranger might rather get stuck than pull this kind of trash.
It's too bad...one thing anyone that has free time is get a trailer and put all the litter in it...it's a pain...but you can ride.