The cache is not at the posted coords, but it is necessary to go there to get the final ones.
At the coordinates, you will find a colorful plaque. Use it to solve for the final:
A is the number of mushrooms right of the one with words on it
B is the number of mailboxes above the plaque minus 2
C is the number of mushrooms plus 2
D is the third digit in the year on the plaque plus 2
The coordinates are N 33 04.AAB' W 117 18.BCD'. BYOP.
You can validate your puzzle solution with certitude.
Congrats to ??? for getting FTF!