OK; the coast range of California is NOT a hotbed of fall color. We have two seasons: moist and green, and dry and brown. Most of the native plants around here (one exception coming up below) try to adhere to the color scheme, except for those hardy few who stay green all year.
Aside from waiting for the rains to arrive, most of the color we get is from yards of folk who have planted a non-native or two.
I took a walk around my neighborhood yesterday (Mt. Diablo foothills in Concord, overlooking the Clayton Valley), and took a few shots.
At least one neighbor has good taste in deciduous trees:

Photo: Don Casey
The transition from brown to green is in full swing. Thanks to a couple of early season storms, the hills are greening up earlier than usual:

Photo: Don Casey
And lastly, if you're really itching for some native fall colors, we have ONE native plant that can be counted on to get under your skin:

Photo: Don Casey
At least this time of year you have a decent chance of spotting the poison oak when you're hiking. Once the leaves drop you're really on your own; when it's green you can spot it, if you know what to look for.