This cache marks the location of nearby benchmark HT3620, a spike in the base of a redwood stump conveniently situated next to a large, safe turnout. You can access it from either direction on Felton Empire. It's also an especially beautiful area, with a creek nearby and a mysterious concrete platform. According to the benchmark's description, the platform is the concrete base of a water tower, although there's no water tower there now. The cache itself is a magnetic nano, which should significantly narrow down the search area.
To find the benchmark, head about 60 feet southeast of the cache location to the large redwood stump next to the road. The benchmark is near the base of the stump in the northwest corner. A bent nail points right to it! There's also a photo in the gallery. You can log it if you're interested in logging benchmarks. Happy hunting!
Congrats to SCStroller on the FTF!