NPS rules generally mean CCW is ok for grounds but not inside buildings, generally like a post office. A little research brought me here...
http://www.nps.gov/inde/learn/managemen ... licies.htm
"Firearms in National Parks
The law governing possession of firearms inside a national park changed on February 22, 2010.
Visitors may possess firearms within a national park unit provided they comply with federal, state, and local laws.
The role of the responsible gun owner is to know and obey the federal, state, and local laws appropriate to the park they are visiting. For more information about Pennsylvania's gun laws, please visit their website.
Please remember that federal law prohibits firearms in certain park facilities and buildings. These places are marked with signs at public entrances."