Good vacation for kids?

I'm looking to take my kids on a vacation this summer, so I'm trying to plan ahead. It would be me and 3 kids (ages 12,14,and 16). I'd prefer it to be something outdoorsy. I don't want to go anywhere like Disneyland, Carowinds, or Six Flags . It can't be any longer than about a week. And it must stay in the USA (no Hawaii or Alaska). Any suggestion would be great!