“Few fictional characters have caught our imaginations as much as Batman, a superhero like all of us in that he doesn’t fly and can’t jump over tall buildings. Bob Kane and Bill Finger created the Batman character, sometimes known as the Dark Knight or Caped Crusader. He first appeared in a 1939 issue of Detective Comics (DC), which immediately recognized the character’s potential for popularity.”
Excerpt from California State University, Northridge at https://library.csun.edu/SCA/Peek-in-the-Stacks/batman .
While not a southern California topic, Detective Comics would have been easily available in the area.