To find this MYSTERY CACHE you will need to find the coordinates that are listed on the inside of the lids of the three caches hidden along the Keyes Farm trail.
Once you have found all 3 caches and written down the info on the lids, then you will need to solve fhe following coordinates:
N42 25.ABC W071 34.DEF
As with all the caches on the trail, there is some decor near GZ to help narrow your search. The container is an AMMO BOX.