Try by Googling Mexico "parish records"

Debra, one of our early members, Marie Northrop wrote the book -- actually wrote three books -- on the early settlers of Los Angeles County. You can do a couple of things: You can join the Society and then request a research lookup (at a reduced member price), you could buy one or all of the books, or you could come into the Library to check in person. You should also get in touch with Los Californianos:

The early Hispanic settlers of Alta California were called Californios or Californianos. Los Californianos was organized by their descendants
to preserve the Hispanic heritage of Alta California (history, music, culture, infrastructure, etc.) and to help other descendants compile their Hispanic genealogy. If you would like to ask questions about Los Californianos or Hispanic Alta California, please fill in the form found in Member Services at www.loscalifornianos.org; write Los Californianos, P.O. Box 600522, San Diego, CA 92160-0522; or e-mail the Web master at LaTejedora@loscalifornianos.org

Good luck on your search, and I hope we can welcome you to SCGS very soon.