After the initial conversation with Casey at the start of the level, take time to explore the Cauldron Lake shoreline. There's a Cult of the Tree stash further down the beach. This can be easy to miss, depending on how thorough you are with searching the coastline.
Location: To get there, go as far as you can along the shoreline. When it looks like you can go no further, take the path into the forest. It might feel like you're abandoning the area, but the short detour will take you to another part of the shoreline previously closed off due to driftwood.
How to Open: For this puzzle it's a memory combination. There is a device connected to a lock, a three-by-three grid of lights. Your task is to memorize the order of the flashes and recreate it once it's over. There will only be about four lights to remember, but if you're having trouble, grab a pencil and paper and draw the path the lights take.
Text Inside: Remember, they look like us, but they aren't. They're like animals. And it's our job to hunt 'em and gun 'em.
Rewards: Flare, Pistol Ammo, Extra Capacity, Small Propane Tank.