The hiking there is awesome. There are several trails from 2-20 miles, take your pick. I have so many great pictures of wildlife and scenery from that park. Camping is good this time of year before it gets hot and the horseflies are in full attack mode.
Like Mike says watch out for rattle snakes. They will really be out this time of year even in the middle of the day on a cool day. At night they are really working. There was one in the campground a few years back. No big deal just be aware.
We stayed there last summer, beautiful place. But yeah, mostly hiking and sight-seeing. No snakes, but some freakishly large lizards and tons of tarantulas. Big hairy jumping monster spiders that would stalk you down and kill you! Or so we thought.