The Campers is started through a dialog with an NPC named Michael in The Watchtower. Danny (the tattooed guy) was killed outright in a volley of arrows by what appears to be the Community's militia for reasons unknown. JD (the guy with the red backpack) fell to his death attempting to escape.
Michael was captured by the and locked in The Watchtower to await the beginning of his own Trial. The dead girl in the Mountain Pass began her Trial there as well, according to the yellowed map. However, after recovering the keys from The High Tower and returning to release Michael, Daphne finds him dead, having taken his own life by hanging himself.
The campsite is located atop a cliff in the Mountain Pass and reaching it requires a series of moderately difficult jumps. At the campsite, Daphne can find a polaroid picture of the young men as well as the Survival Guide - Viper Bite document.