One of the Premier MTB races in Northern California the Lemurian Classic is a great race held annually in June. There is a long course which is a single 26 mile long lap, a shorter 20 mile loop, and the beginners loop is 8 miles. There is no sandbagging at the Lemurian, you chose which course to race on and a Pro class but otherwise it’s just simple age sex categories. Even better, the Lemurian course is mostly singletrack.
The real kicker that makes this the king of Grass Roots racing is the fact that the proceeds from the race all wind up going directly to improving the trails in the Whiskeytown/ Mt Shasta Area. Combine this with a great great atmosphere, awesome trails, and a laid back group that puts on the event and the $35 entry fee is dirt cheap.