Great Thread ! I come back to read a few pages every month or so. As mentioned earlier, there's little tangible California history much older than 100 years, except for the tourist traps. I'm jealous of you guys in the East.
I came across these cabin ruins a couple years ago on the Palomar Divide road, an easy mountain trail near San Diego. I researched it and turns out it is a mining cabin built around 1930 for the Ware gem mine, used into the 50's. Made of local rock and cement, but no roof remains. The mine entrance is closed off. Also interesting, but not as visible, just a short hike away, there is a ground level covered cement water tank fed by a catch basin presumably used by the miners. I believe it was marked with a 50's date. It's always full when I've been there and newer galvanized piping has been installed. I'll take a pic next time. There's some rusty mining remants in the area, but nothing major.