There's an Area Challenge for the Wildlife Exploitation Preserve; "Mordy's Secret Stashes". Where are the three stashes for this?
All three stashes are in the Stalker pen immediately after the first Skag Pen where you have to jump down from an overpass.
The first one is to the right after you leave the building to enter the Stalker pen. Stand under the overpass and look West, between the support columns you'll see a gap and some Hyperion crates. Enter the area to mark it completed.
The second is under the waterfall, which is the source of the river in that area. Just walk under the waterfall and you'll find it. There's a Hyperion weapons locker here.
The third one is near the north end of the overpass in that area. Climb up the rock formation in the east side of the area, then travel northwest. You'll see a giant mushroom to the north that you can reach. Run-jump onto the mushroom, then jump west onto the cliff face. His stash is here with a Hyperion crate. There's another weapons locker here.
As a sidenote these chests respawn (though there's nothing good in the first stash, just ammo/cash) so you can visit them every time you go to the preserve.