I've lived in CA since 1962, and in southern California since '67, but I'm still a "young man", so Koufax, etc. are before my rooting/viewing era. For me:
Basketball: Magic. Enough said, but I will listen to arguments for Larry Bird.
Hockey: Gretzky, although he was more dominant in his earlier years with the Oilers.
Women's Track: Jackie Joyner-Kersee
Men's Volleyball: Karch Kiraly
Supercross (believe me, this is a sport) Jeff Ward
Men's Diving: Greg Louganis (don't chuckle, this guy DOMINATED a sport now owned by the Chinese)
Here's a new category: Greatest coaches ever in their era, regardless of sport: Pat Riley, NBA w/Lakers, Phil Jackson, NBA w/Lakers and John Wooden
Players who for a "shining moment" were most dominant, but not over many years:
Football: Eric Dickerson: Rams (still holds that season rushing record)
Baseball: Fernando (that guy was pretty crazy good for a while, wasn't he?)