I live in Southern California and we do have good cycling here all winter long. If you are looking for areas where the population is not so dense, you may want to look in Ventura County, Santa Barbra County or even farther north like Monterey or Santa Cruz.
Ojai is in Ventura County and there is some nice riding there. The attached link will show you a topo map and photos from a century ride.
http://www.ojaivalleycentury.org/