There's an imaginary line that marks southern California and that is the northern most border of Kern County, Riverside, San Luis Obispo County and San Bernardino County. The latitudes of these counties even on the shortest days of the year have more than nine hours of glorious warm sunlight which makes it most possible to grow almost any crop during the winter months. Most avid vegetable gardeners in these areas take advantage of the moderate temperatures that are similar to Mediterranean climates of Turkey, Italy and parts of Spain and Portugal.
Like I always say, when in Rome.. . grow it! Besides growing the regular cabbage, beets, bok choy, various lettuce and onions, I can get away with growing tomatoes outside until December. Herbs love southern California and the sunbelt during the winter months as well. My basil and oregano flourish more so in Autumn and Winter rather than Summer or Spring.