This passed in Washington state, too.
We had a discussion at the ranger station last week, what are we going to do when 400 college kids come up to the ski area on National Forest land and light up, thinking they're in Washington state, must be legal, right? No one wants to bust 'em all, but we're required to uphold the law. So for now, we may have some signs made up and put on the highway heading up the hill, something like "Entering National Forest land, marijuana use prohibited", at least put 'em on notice. Don't know the answer yet for the rest of it.
Some of the other posters are quite right, you do not want to be found with a firearm and a controlled substance, you will have serious problems, one of which is your firearms, all of them, will be confiscated.