This mission unlocks after you take over the outpost The Hornet's Nest.
Enter the house and talk to Willis. After the conversation, collect the tracking device.
Drive your car towards the marked spot. In the spot, where the fence is destroyed, go down the hill (the screenshot).
Once you are down below, take a photo of the package shown in the picture, which you can find in the area marked blue on your mini-map.
In the next search area, the package is among the branches of the tree, to the left.
In order to get to the third package, you need to shoot the padlock on the shipping container shown in the above screenshot. Swim inside the container to find the third package.
The next package can be found on the beach, near the rocks.
In the next area, jump down the waterfall, into the river below. As you swim down the river, on the left you will notice the vine shown in the screenshot. Climb it to reach the ledge.
Jump over to the next ledge that vine is hanging from.
Before you jump over to the next ledge on the left, kill the snake on it. Go right and jump over, onto the ledge behind the waterfall (the screenshot). That is where the last package is. Taking a photo will conclude this mission.