Not sure the latitude of Northern Cali, but I am in souther SD, and I think my pullets will start the second week of January. around the 14-16.... that is what has happened in the past. Right now, no eggs, ugh! Within days of mid January, I will be getting scads.
That is my vote, if you are close to that in latitude.
Maybe a tad lower then you but I wouldn't be sure either with out checking a map. I have 3 girls (of 6 total) that are about 7 months old give or take. One started laying about 2 weeks after we got then and the other 2 are just holding tight. miss marshall just doesn't seem to want to lay yet. But the third looks mostly black astrolorp so I'm expecting her to take her time too. I have 2 young pullets also they ares probably close to 12 weeks now. I'm expecting eggs from those 2 later January early February