Far Cry 5 > Prepper Stash Locations and Walkthroughs
Stash Mission Start:
You'll find the note at Rattlesnake Trail Bridge. We're looking for a crashed plane.
Investigate the plane crash:
Follow the path over the bridge, up the mountain. At the dead end, grapple up.
Up at the top there is a path leading down. There are some sticks with red tops. Between two of them there is a blue rope climb point. Go up there and continue climbing. At the top you'll see the red sticks again. Follow them as you climb up.
At the grapple with the broken bridge, swing over towards the waterfall. There you can climb up to bridge level.
Cross over at the broken bridge and continue the path up, following the sticks. Grapple swing over at the second broken bridge. Then grapple down on the other side.
Follow the path across the waterfall, up the stairs. Another grapple swing at the dead end. Then a grapple up.
Now we're up at the crashed plane. Find the key. Its at a box near the tail end way up the path.