Some years ago while hiking in the Catskills we went off trail and found a nice rock outcropping near a summit. That spot afforded us wonderful views while having lunch. While sitting on the outcropping I found an un-clenched horseshoe nail... I assume it was left during the earlier logging of the Catskills.
It doesn't matter where I go... Catskills, Adirondacks, Rockies, Everglades back country... I find signs that people were there before me!