This is a simple two-stage multicache, with a bit of history at the start and a fantastic view at the final.
At the posted coordinates is a large plaque. There you will learn a little history of the Island and determine the final coordinates for the Geocache.
The coordinates for the final will be arrived at N 37° 51.ABC W 122° 26.DEF where values for A - F will be found on the plaque.
A = "The Packet San (number of letters in name)"
B = First digit of date "September __"
C = Second digit of date "September __"
D = First digit of year, bottom of plaque
E = First + forth digit of year at the top of plaque
F = Second digit of "California Registered Historical Landmark No. ___"
A + B + C + D + E + F = 23
From the marker it is a considerable hike, with some elevation gain. Be sure to dress for the island in layers, bring energy food (such as an energy bar or fruit) and at least one litre of water. The final is a camouflaged ammo can with log book, writing tools and some trade items.
Happy caching and enjoy your trip to the island!