It's the sounds of billions of people shooting their way through National Parks today. Blood will run in the pine needles, Yogi Bear will be riddled full of holes while searching for picanick baskets, and Old Faithful will be used for target practice.
At least, that's what some of the screeching from the anti-rights bigots sounds like.
Update
Apparently, it's a PSH holiday!
Then that calls for one of these