If you're of substantial build, carry a large knife (Kabar was originally named so because a fur trapper wrote them and noted how good it was when he had to 'kill a bar'). If not, carry a pistol in a substantial caliber/energy at minimum. .357 magnum, .357sig, .40s&w, .44mag, and any of the larger and more ridiculous would work fine. A levergun in one of those pistol calibers (like a Marlin 1895) would work well too, as would any rifle in a hunting caliber or military caliber .30+.
Note that due to an amendment to the recent credit card reform bill, the concealed carry laws of the state now apply to national parks in that state.
That said, I did read a story of a woman who encountered a black bear and ran, for about 2 hours, back home while engaging in a running fistfight with the bear. She was scratched up but okay. Of course many people just get killed by them, too.