As a California ex-patriate, I am SOOO jealous. I went wine tasting here in Virginia a couple weeks ago. There is absolutely no comparison.

Some of my favorite wineries are:
Cakebread -- by appointment only
Praeger Port Works -- a must if you like port!
Markham -- one of the best Merlots I ever tasted was from here
V. Sattui -- they have a very tasty madeira
Cosentino -- everything they make is tasty

Many of these are further north -- St. Helena and beyond. Worth the trip, though.