RideSB.com has announced the 2007 Firestone Walker MTB Classic for April 27 - 29th, 2007 in Los Olivos, California [ MAP ]. This race offers cross country (XC), marathon (5 laps of the XC course, around 75 miles) and downhill (DH) events. The events run the entire weekend, with a variety of non-biking activities also.
In the past, I haven't covered races this far south (i.e. just north Santa Barbara) but it seems like a lot of people headed down for this race last year.
UPDATE: This is now a NORBA event.