When the area is clear, drop down to ground level and go to the northern corner of the area. When the enemies stop coming, look around the area with your rifle to see if there are any other not-zombies hanging out in the alcoves of the cavern. The not-zombies will climb up to the tracks platform where you can easily take them on with your pistol or shotgun. There are yet more enemies in the area, and your best bet against them is to wait on the mine tracks and lure them towards you. Take 'em out and continue down the mine shaft until it opens up to a large cavern.
Just around the first bend of this mining tunnel are a few not-zombies.
