- Never given much thought about a backpack beside the trail being a crime scene...Then again in this day and age, you just never know and the less disturbance of the pack and immediate area, the better.
in my hiking area - los padres national forest - marijuana gardens are constantly being discovered. the forest service et al took out over 28,000 plants from just one location in august 2010.
the 'garden guards' carry automatic weapons. imagine being caught looking through his backpack when that 'garden guard' returns from a nature call...
on the other hand, at the junction of the main mt. whitney trail and the john muir trail, just a short slog from the mt. whitney summit, it's not uncommon to find 10+ backpacks left behind while the summitteers summit.
i still wouldn't touch a pack, but i would contact authorities as soon as possible.
situationally dependent.