The California State flower is the Eschscholzia californica. Known as the California Poppy or Golden Poppy, it is springing up everywhere. Here in San Francisco, it grows in the cracks of sidewalks and roads and can be found in all the parks. It varies in color from white to dark orange.
UPDATE: Ed Brownson added this gem to the Bernalwood Group on Flickr:
PHOTOS: Julie aka Rudha-an, Ed Brownson