Far Cry 5 > Prepper Stash Locations and Walkthroughs
Stash Mission Start:
There is a note inside Taft Lookout Tower.
Go to Raptor Peak Trail:
Follow the trail to the mission pointer up the mountain. Then the climbing starts. Follow the blue rope.
Get up the mountain by grappling and climbing. Follow the path, look for blue/green ropes or grapples. Sometimes you'll have to crouch and then grapple again...
Then through the cave and grapple on the other side.
Then balance over the tree trunks - twice. Then grapple again on the other side.
As soon as you're up, a lot of eagles will attack. Now, no more climbing needed. Find the tent around the corner. The stash is behind it. Here's the map in case you want to skydive / use a helicoper or plane instead: