Planning for fall: When does Fall Start in Southern California anyway?

In the book "Square Foot Gardening" by Mel Bartholomew,
 (http://www.amazon.com/Square-Foot-Gardening-Garden-Space/dp/1579548563/ref=sr_1_3?ie=UTF8&qid=1374863110&sr=8-3&keywords=square+foot+gardening)  I found a fantastic table that details growing from seed, transplanting and planting seeds, growing time and weeks of harvest, when to pull and replant with something else, all detailed by weeks before and after the first and last frost. 

It got me thinking:  When does fall really start in Southern California?  We don't have defined seasons like other places in the country, or even here in California.  Northern California has much more defined seasons.  Here in the desert, it's just hot, then less hot, then hot again.  I don't mind it.  I lived in Southeastern Pennsylvania for seven years, and I got my fill of seasons.  Just think of how long the gardening season is here!!! 

I did some research and came up with this:  We don't really have much frost.  Last Fall/Winter, the first date that dropped below freezing was January 12th, at 28 degrees.  It never stayed below freezing for more than a night.  This says to me, that with a couple of floating row covers, I could grow fall and winter veggies until the spring!!!  There isn't a sleeping season at all here. 

But in terms of planning, I wonder at what point to plant stuff - - there isn't a "first frost" marker to go with. 
Historical temperature averages: (as detailed for Ontario, CA by Accuweather.com)

October:  HI: 77-80  LO: 50-60
November: HI: 68-74  LO: 45-50
December: HI: 68-78 LO: 45-55

Hmm...  I'm going to have to think on it a little, and work out my own chart.  More to come.

Green thumb out.