Here is the full list of all 10 Firewatch achievements worth 1,000 gamerscore. It takes around 4-5 hours to unlock all of the achievements on Xbox One.
Complete Day 1
Complete Day 2
Complete Day 76
Complete Day 77
Complete Day 79
Fill a disposable camera with photos.
Have a hands-on encounter with the local wildlife.
Find a bee.
Adopt a turtle.
Find and hear the recording of the song "Ol' Shoshone."