Pest Filled Mine is a side-quest Quarry area you will have to cross while playing the Historian -Roots mission, and it includes only one Outriders Loot Chest. The Outriders Quarry Pest Filled Mine is relatively small compared to other regions; however, in order to complete the said quest, you also have to inspect the Flooded Buildings. So basically, the mine is the area between the Outpost Gate and Flooded Buildings.
To enter the Pest Filled Mine the first time, you have to track the Historian-Roots side quest or mission. Your first goal is to set your camp in the Quarry; then, you’ll have to fast-travel to the Outpost Gate Explorer Flag, collecting the chests in the process.
From there, simply follow your objective marker, and you’ll eventually reach a broken bridge. Jump over the gap, and you will enter the Historian-Roots Area, which is, in fact, the Pest Filled Mine.
Although a small area, the mine, as the name implies, is overrun by Perforo, so expect heavy resistance. Regular Perforo, Venomous, and even Alpha Perforo will attack in waves the moment you reach this specific zone, so stay alert.
Loot Chest Location
This Outriders Loot Chest is extremely easy to find because it’s in the starting area. Once you deal with all Perforo that come through the mine ahead, look for the ammo crate, and next to it, close to the rock, is the chest you’re looking for. You can see it in my screenshot below.
Once you get this one, restock and push forward through the mine. Eventually, on the other side, you’ll have to clear the rocks in order to advance. The moment you exit, you’ll enter the Flooded Building, where the next chest awaits.