Another way to get old coins in So. CA is to study for beach erosion. Tides + on-shore swells, + on-shore winds = beach erosion. When that happens, it can produce old coins. Trouble is, that might be few and far between, and you have to know how/when to be there at the right time. Also some past erosion events (1982-83, for instance) cut in so far, that it's seemingly all clad now (albeit copious amounts, and albeit chances at jewelry) in modern erosion events. Still though, I see occasional posts of guys who've still gotten silver during erosion down there.
There's also even some spots on the dry sand that can give up silver coins (albeit perhaps just 1940s/50s losses). This is because during the 1940s/50s, the army corps of engineers went up and down the coast there, doing jetties ever few miles . And various harbors walled in, etc... This had the effect of trapping the dry sand zones , on some beaches, such that it never erodes in or out ever again. But in those zones, you'd need to go 1 ft. deep or deeper. So you'd need something like a pulse with big coil, or Sov/Wot combo. But I know a guy who got over 100 silver coins from a certain dry sand beach doing this trick, listening for whispers. At other beaches, the dry sand will be strictly fill following erosion of past decades. And would be hopeless to ever find an old coin there . So you just got to know where the trick works for certain zones that have remained un-disturbed for 60 to 70 yrs.