Welcome to Tnet. I live in Stockton CA. Once in a while I will get up to Sacramento, but I am not really familiar where to go, but I would more than happy to call you next time I intend to go up, to see if you would like to go metal detecting.
I am a member of both.
As the name suggests, the Gem Society is geared more towards geology and rocks, while the Buffs club is dedicated to metal detecting.