This California Native Plant Society site has a lot of information about native plants. You can search by region to see what naturally grows in your area. A little bulky, but worth the work.
"Our goal at Calscape is to help Californians restore nature and save water one garden at a time. We do this by showing people which plants are really native to any location in the state, helping them figure out which ones they want, and where to buy them and how to grow them."