Answer: The autumn color you enjoy so much is brought about by cold weather - something your southern California garden cannot provide. (Which is why the hawthorn you're looking for isn't available in your area.) For dependable fall color you can plant Sweet Gum (Liquidambar). The bark is interesting and the non-descript flowers produce prickly fruits, but it doesn't provide the 4 season interest you desire. Maples will provide autumn color, but not spring bloom. Pyrus, ornamental pear, will flower in spring and have colorful foliage in the fall, but not berries in the winter. There are several trees with spectacular spring bloom, but not fall color or winter berries. (Flowering cherry, Empress tree, Catalpa to name a few.) It's a difficult situation - wish I had more suggestions for you!
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