Mining the Depths is based on the Cave level in Chapter 2 of Jake's campaign. It has five time bonuses and two combo bonuses. The starting waves consists of Zombies with an idling Shrieker, Zombie Dogs and undead BSAA agents start showing up as you kill enemies. Bloodshots and armored zombies holding magnums and assault rifles will also spawn.
The hidden boss in this stage is the Strelats and it will only spawn if the player kills 70 enemies before 10 minutes have passed.