I'm in northern California, too. There's a gifted magnet called North Star Academy in Redwood City. Its website is thin on details. A review on greatschools.org damned it with faint praise by noting that "the kids have to test in, which weeds out low performers."

I knew someone whose son attended. Lots of homework, and (at the time, a few years ago), and attitude that "they're all the same until after third grade, anyway" when speaking of giftedness and gifted kids.