The cache is not at the posted coordinates. You can get the coords by completing the Adventure Lab Arcata Marsh.
Marsh Trail Hours: The Arcata Marsh and Wildlife Sanctuary is open to the public every day from 4 a.m. until one hour after sunset.
The Arcata Marsh & Wildlife Sanctuary is an innovative wastewater treatment facility for the city of Arcata. Its 307 acres is a paradise for bird watchers with over 330 species spotted within its boundaries. The five miles of trails offer excellent hiking, biking and dog walking (leashes required).
You'll need to bring a pen to sign the log.
You can validate your puzzle solution with certitude.