I was hiking up to a cache and I "discovered" these neat old arrows. I knew offhand that they were used for airplane navigation. It turns out they were part of the Transcontinental Airway System directing planes along the transcontinental airmail route. This example is extremely rare because it is a double arrow. The double arrows guided the airmail planes for both the Chicago to SF Route and the Seattle to LA Route. A vast majority of the arrows found are single arrows. Each location had a light beacon and sometimes a small shed. You can see some of the metal remains. The arrows pointed the way to the next beacon. Pilots simply flew from arrow to arrow.
For more info and links to other arrows just Google "Transcontinental Airway System".
Anyway, hike up to Stage 1 and look around. For some strange reason, the bench disappeared so the answers are given.
Cache can be found at N37 54.ABC W122 04.DEF where
A = Number of Benchmarks found on "beacon slab"
B = Number of Arrows, multiplied by 2
C = Number of Slats on Bench plus number of Arrows C=7
D = Number of "Feet" on Bench D=6
E = Number of Slats on Bench E=5
F = California Division of ____________. Turn first letter into number equivenent.
Checksum A+B+C=12 D+E+F=19
You can validate your puzzle solution with certitude.