I was walking around in the nursery and noticed that there's always something for the insects and birds, even in Early December.
December is kind of the spring for California as the rainfall pattern normally, (used to anyway) gets the ground wet from December to maybe early April. If you do not have deep roots or are plugged into a spring the ground is dry by late spring. Better to do your thing in the snow.
So you have a few wet months to produce flowers, leaves, new growth and maybe a few berries or fruits. A number of the native bees are already out, most noticeable the Anthophora , Digger Bee.
SOooo, planting now is easy for the plants and makes them happy. You may grimace at the thought of getting wet, but there are breaks in the storms just for you and your shovel. The air is clean and the dirt smells wonderful!