Head to the Lost Coast. You can do a mixed loop out of Shelter Cove that can be part gravel/dirt roads and part pavement. (There aren't any cars on the pavement to speak of.) Head on over towards Honeydew and either camp at Camp A.W. Way or head on down to the beach again from Petrolia. Wilder Ridge is paved, the north/south roads to the west of it aren't.
There's also the option of an out-and-back along Usul Rd (dirt) and Chemise Mountain Rd (mostly gravel the last time I was on it years ago).
The Lost Coast is all hills, all the time, so be geared low and have good brakes.
Plumas N.F. northeast of Quincy. Great roads - mix of paved, dirt, & trails.
Frequent enough campgrounds so that you can get water without filtering.
But, of course, you can camp anywhere - but check fire regs this time of year.
Taylorsville, Genessee, to Beckwourth - and lots of loop possibilities.
Relatively light use by Calif standards - no eye-popping scenery -
Valleys and streams, low mountains, meadows.
Diamond Mtns escarpment over Honey Lake Valley is nice.
Also check hunting seasons - archery has started I think -
If you ride in this area - have something orange.
The higher areas should be chilly in the a.m., warm afternoons.
Not appropriate after mid to late October.
Hmmm - Nov/Dec means south.
And you have to be careful because some of the dirt roads turn to glue when it rains.
Fall is a pretty bleak time in the desert after a summer's heat.
(Although this year some areas have gotten rare summer rains.)
I'm thinking Carrizo Plains Natl Monument - east of SLO. http://www.blm.gov/ca/st/en/fo/baker...s/carrizo.html
The Coast Ranges of Monterey, San Luis Obispo, Santa Barbara, and Ventura Counties do have a network of paved and unpaved roads, also. The sticking point would be whether they have a wet or dry autumn...the Cuyama Badlands and the Mt. Abel highlands are an interesting area, too, but the washes may be a bit too sandy.
I agree about going south, the weather could go either way in the north. In early December here (2,000 feet elevation, near Chico) you might get temps in the 40s and almost constant rain for a few days - or worse - if a cold storm moves through.
Take Caltrain up to sf. Hit the Marin headlands, you can almost link dirt all the way to pt. Reyes. Look for Bolinas ridge on a map. Indians road out of Arroyo Seco is good. Henry Coe is always nice but steep. Coit road is a fire road that isn't too bad and can get you out in the park. Plus it's super close to you.