I spent 3 days hiking and camping in Yosemite National Park with three guys I met on Couchsurfing.org .
Half the park was shut down due to forest fires and on the way in there was a blanket of smoke covering the road and the forest on both sides of the road was still smoking.
We thought maybe we had made a mistake trying to go but eventually when we got deep enough inside the park the smoke dissipated and we had 3 great days of hiking.