New regs on carrying in National Parks and Wildlife Refuges
Pdf of final rule here. They go into effect on January 9. The actual rule is two paragraphs long, at pp. 74971-72, and says that a person may "possess, carry, and transport concealed, loaded, and operable firearms within a national park area in accordance with the laws of the state in which the national park area, or that portion thereof, is located, except as otherwise prohibited by applicable Federal law."
The other para. applies that to National Wildlife Refuges. Neither applies to State or local parks or refuges. Looks as if carry has to be concealed, which in most States means a permit, although the rule itself does not refer to such permits.
UPDATE: I'd guess that "for a lawful purpose" is a general term that has a simple meaning -- for any reason not forbidden by law, such as committing a crime.
Hat tip to reader Carl in Chicago.