Buried way down at the bottom of HR 627, the Credit Card Protection Act of 2009, (the full text can be read here: GovTrack: H.R. 627: Text of Legislation, Enrolled Bill )
somebody snuck in a bit about carrying on certain government lands, such as national parks.
If you read section 512, it states:
"(b) Protecting the Right of Individuals To Bear arms in Units of the National Park System and the National Wildlife Refuge System- The Secretary of the Interior shall not promulgate or enforce any regulation that prohibits an individual from possessing a firearm including an assembled or functional firearm in any unit of the National Park System or the National Wildlife Refuge System if--
(1) the individual is not otherwise prohibited by law from possessing the firearm; and
(2) the possession of the firearm is in compliance with the law of the State in which the unit of the National Park System or the National Wildlife Refuge System is located.
So it sounds like you might be all set. I'm almost certain this bill passed, but I'd still double check if I were you. It's fresh (and under reported) enough that the folks doing the enforcing might not be familiar with it yet.