Parsons, WVA might have some decent trails. Depending on where you are i Pittsburgh, it might be about 2.5 hours from you. The area all around Chalk Hill, Ohiopyle, Farmington, etc. is mostly state game lands. We used to ride our 4 wheelers out around there but we took the risk of getting shot.
Well, due to the large number of abandoned strip mines around the area, it's not hard to find a place to go offroad, but I'm not aware of any LEGAL dedicated 4x4 parks here. I can tell you there are places up north (near Benezette PA) where there are miles of trails & 4x4 roads. Good luck.
Give Rock Run a try. I took my ATV my first trip there to scope it out, and its 100% legit. 90 miles of trails. Make sure you gas up when you get off the interstate 99 because you won't see another station for 30 mins.
I've been looking for places that are legal and theres no chance of getting in trouble for riding or wheeling. Every where i used to go ends up with someone getting in trouble after we have been going wheeling and riding there for years.
Hopefully once the weather breaks i can make it to some club events and what not.