The posted coordinates will take you to a utility pole, which is the starting point for this and the other two multis in this trio.
This multi will require calculating a couple arithmetic averages.
On the utility pole, you should find a six digit number oriented vertically under the letters "UD". Reading from top-to-bottom, call this number ABCDEF.
To get to the final stage, calculate two averages to solve for X and Y that complete these coordinates: N38 39.X W121 18.Y
X = average CCE, DEF, E
Y = average ABCE and EDE
Checksum for the six digits in X and Y is 27. (The final is in Del Campo Park.)
These are the other two caches in the trio that have the same Stage 1:
GCB1R92 (Easy Peasy)
GCB1R95 (Projection)