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."
California Native Plant Society (CNPS)  Lots of resources and recommendations.
"We’re on a mission to save California’s native plants and places using both head and heart. CNPS brings together science, education, conservation, and gardening to power the native plant movement.
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CNPS Northern San Joaquin Valley website.  Look here for local chapter information and plant sales.  Lots of additional information throughout the CNPS website. 
"The North San Joaquin Valley Chapter represents Merced, Stanislaus, and South San Joaquin Counties.  All are welcome to join in our activities. We also host a bi-annual native plant sale. Please peruse our site and see what we have to offer!"
Brugger Design.  Need design help with your native landscape?  Jim Brugger, with the California Native Plant Society,  specializes in designs using California Native Plants.  Contact Jim at:
The Theodore Payne Foundation is a great organization and resource to help you garden with California native plants.
"The California Native Plant Wiki is an information resource created by the Theodore Payne Foundation to help you garden with California native plants. The Theodore Payne Foundation is a non-profit organization dedicated to promoting the use and understanding of California's extraordinary flora."
Looking for additional species or to have them shipped to you.  One of the best resources available is Las Pilitas Nursery.
"100% California native plants shipped to your front door.  Since the 1970's Las Pilitas Nursery has been growing, researching and planting California native plants. We do the work, you get to play with the plants and enjoy the resulting web pages."
Wildflower and Plant Identification - Interested in identifying wildflowers in the field?  This is a great resource.  Download the app for your phone.  Free.
Wildflower and Plant Identification - Another app you can download to your phone for identifying plants in the field.  Free in the Apple App Store.  Also available for other parts of the State and Country.