For the most part, you may not
carry in National Park visitors' centers, souvenir shops, concession buildings, etc. I copied this from ZeSpectre over at GRM:
Q: What about information stations and concession stands?
A: Any restricted federal buildings must be clearly posted as such.
The interior of a federal building (this includes any rest stops, information centers, and concession stands bearing the National Park Service logo) falls under Title 18, Sec 930 “Possession of firearms and dangerous weapons in Federal facilities” ( http://tinyurl.com/yg2zhwb )
However, Title 18, Sec 930 does stipulate the following
(h) Notice of the provisions of subsections (a) and (b) shall be posted conspicuously at each public entrance to each Federal facility, and notice of subsection (e) shall be posted conspicuously at each public entrance to each Federal court facility, and no person shall be convicted of an offense under subsection (a) or (e) with respect to a Federal facility if such notice is not so posted at such facility.
So there shouldn’t be any confusion as restricted buildings MUST BY LAW be “posted conspicuously” that weapons are not permitted. If it’s not posted, it’s not restricted (Unless you have been notified by an authorized person and asked to leave because then you've had "actual notice" under subsection H...<sigh>).
So, they have elected to treat these facilities the same as any federal building - no weapons of any kind. I was at the Grand Canyon in May - I carried everywhere I went, but was balked at the bookstores and visitors' centers because they were, in fact, "posted conspicuously" with "no guns" signs. So, I relieved myself in the brush. Sue me.
Oddly enough, the El Tovar Lodge was not posted, so I carried there where we had a lovely dinner. An outstanding restaurant, redolent with history. Two thumbs up.