Simply solve the following code and the coordinates will be revealed.
N1C866EMGXR
Make the obvious corrections based on GZ being within a mile or so of the stated coordinates. Choose Magnolia for the easting.
This cache also contains a hint for another puzzle of mine - Exercise for mind and body which is rated as 5/5.
The cache contains an unactivated trackable for the FTF, as added incentive.
Parking is available at the start of the path to GZ. Please ensure the cache is hidden well when you replace it.

Congratulations to Benjw for the first time find. This is one of those puzzles where you either get it or you don't!