I know of 4 "private mint" CA gold coins that have been found. I'm sure there's been a few more, but just thinking of those 3 off the top of my head. 2 of them were guys I know: 1 was found by Jim Owens, in Monterey, CA, during the winter beach storms of 1982:
1) A $5 Schultz gold piece. Turns out, it was only 1 of less than I think 10 or 12 (?) known to exist. He sent it to auction the following year (1983) and it fetched $45k, if my memory serves me right. That was a LOT of money in 1983 (you could probably still buy a house around here for that price, back then

Heck, I wouldn't argue with $45k even now, ~30 yrs. later
2) There were two "Moffat" gold coins found in a park scrape/renovation work, in an old town park north of SF (Santa Rosa, if I recall). That was about 12 yrs. ago.
3) There was a private mint gold coin found on a mud-flat beach, where demolition spoils had been dumped over the years, on a beach inside SF bay, near SF airport Brisbane area. Not sure exactly what coin it was, or exactly which beach in that area.