There's a very active racing community in all of California (north & south) with races every weekend between January and September (and then cyclocross starts). Because we can ride year-round, you'll find many pros live in California, so the competition is tough. There are more women racers in either of these two districts than in any other districts in the country. Women's fields are typically large and it's challenging to place well and upgrade. Both northern and southern California have women's development programs (series just for beginning women racers) and lots of clinics and other fun stuff too!
You can find information here --
http://www.ncnca.org
http://www.scnca.org