From Ehom Bear Tolls is the first Hidden treasure mission in Far Cry: New Dawn. You learn about this stash in Prosperity after you leave the main building. Its location is marked on the map below:
You will find an abandoned church. There are three bandits inside - one of them patrols the terrains around the cages, the other two are standing on the rooftop. You shouldn't have problems with eliminating them. Read the note lying on the small stall in front of the church.
You learn that a bear has the key to the stash. You need to summon the animal. Reach the bell tower and either shoot or hit the bell.
The bear is a tough opponent. A single hit will deplete about 1/3 of your health bar. However, the animal will need to get closer to you first. Keep a safe distance to avoid damage. Sprint and turn around from time to time to shoot at the bear. If you just walk backward, the bear will be able to catch you.
Kill the bear and take the key to the stash. The treasure is inside the hole behind the church. You will find components, duct tape, perk points, and a journal. If you know how to open locks, you will get titan.