I'm not from PA, but I have some jeep buddies from that area in PA. They come up to MA every now and then to camp out and wheel. I've heard them talking about some mines that they can wheel in. Some you can get permission to wheel (and I would assume ride too) in, some you can't. I'd find out if the ones you want to go to you can get permission first before trespassing and ruining it for others.
Now that I think of it, one of my friends just shipped off to Ft. Leonard Wood!! PM me if you want to get in contact with some other guys who may know the legality of some of the old mines. From pics, they look pretty fun for wheeling (jeeps), but it looks WAY more fun for a quad or bike!!