You will probably loose reception about 10 feet into the cave, so I will give you the approximate location of the cache.
As you go into the cave you will see three sections/portions, one on the right, one straight ahead, and one immidiately to your left.
You want to take the "sub-cave" to the left and go down about 15-25 feet.
Once you are down there the cache is to your left under an overhang of a rock. The cache is a ammo can.