I have the same question... The only places I know of are New Trails Rd (over in the york area). Rousch Creek and there is a thread in the PA section for Anthracite Adventure Park (not yet open yet)...
I'm still finishing up my build, so I haven't hit any of these places yet. I'll be looking to start hopefully in a few weeks
Anthracite Coal Company will grant 1 year land use for about $100. The land use applies to many of the reclaimed land all around PA. Some areas can be really fun, but there is still an inherited danger. Best to use your judgment and don't go alone.
The one by Altoona is clad big merf if that's the one u are talking about we hit that up from time to time we mostly run at the sand plant in imler or my family has some private land that a pipeline runs across down in buffalo mills. Any one is welcome to join us.