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.