The Native American cultures here in SoCal took quite a hit, and were profoundly altered, but I don't think "destroyed" is quite apt(although close). I know many Chumash here locally, and their cultural ways are undergoing a rebirth.The story goes that the Northern Channel Islands were abandoned following the 1812 quake, although there were many other factors in play as well.

Today geologists can excavate fault zones, find evidence of past events and date them, along with some notion of their magnitude, so we do have some idea of past events.

The traditional Chumash explanation for quakes is that the two giant snakes holding up the earth shift and move about, causing the ground to shake....
Geezer in Chief