In Firewatch, there are notes to be found throughout the map which can tell Henry more about the past.
Summary[]
Note from Dave 7/7/86 can be found inside of Cache 306.
Text[]
7-7-86
Ron,
Hey man, guy couldn't take it so I locked up his
lookout and put some stuff in the box.
Found one of those bars you liked. Hiking into the park but lets get fucked when I'm back.
Dave