These light, intermittent rains that have been passing through the Bay Area are just what we need for Fall planting. Especially with our infamous clay soils, just this little bit of moisture loosens things up just enough that the nutrient-rich clay particles don't shatter when we dig into them; yet the soil's not so waterlogged that the clay gets compressed and compacted by our work.
This is an ideal time of year to add organic matter (the best "clay buster there is!), whose nutrients and microbes will leach a little deeper into the subsoil with every rain. It's also the best time to get new plants into the ground (particularly California natives), who will use our long, mild winter to develop a robust root system. If you succeed on both counts, your spring garden will be amazingly healthy — and amazing to behold.