metal addict, I am familiar with your part of CA. And If I were you, I would be putting my research into the defunct picnic grounds/resorts/campgrounds of your area. Because, as you know, your area of CA was the "playground" for SF and bay area folk. Scores of old mineral spring resorts, campgrounds, fraternal grounds, picnic groves, etc......
If you can find those that 1) went defunct early on (as opposed to continuously operating parks to-this-day, and/or covered by modern home-sprawls), 2) haven't already been researched and hammered by other md'rs, then you could do good.
These type places far-&-away blow the doors off of ghost towns, as far as coin-ratios go. I've heard of hair-raising stories of guys from the San Rafael & Napa areas, in the 1970s/80s, that were the the first to research and hit these type spots up there. And they scored big time on old silver. I'm assuming they didn't get to all such spots there. Today's research ability (the internet, old newspapers at your fingertips, etc...) can lead you to some more obscure ones perhaps.