Michaux State Forest, I camp and ride there a lot. lots of great dirt roads to ride.
I do take my ATV with me and ride the ATV trails when I camp there also.
get a map from the office or download one, you can easily do 150 miles of dirt roads in a day.
also check out AOAA http://www.anthraciteadventure.com/pages/
Anthracite Outdoor adventure area