California has more motorcyclists than any other state. If you're a rider and you want to ride with the locals, here are some good opportunities.
Moto Shop in South San Francisco is a gathering place for the motorcycling community - they rent bays and tools by the hour, complete with motorcycle lifts, so you don't have to do mid-tour bike maintenance in a hotel parking lot or campground. They also offer seminars, host barbecues, and frequent group rides via Bay Area Moto Group. Check them out!
Pashnit is passionate about motorcycling Northern California. Here's what founder Tim Mayhew hears the most: "How did you find this road!?" He turned his passion into a business creating detailed maps of the best motorcycling roads in the area, and gives a select number of tours a year. You show up and follow Tim... they're great, budget-friendly, and truly inspired.
The name might not sound appealing, but if you want to get a load of what's happening with motorcyclists here in the San Francisco Bay Area, you could find something great by perusing BARF. From rides to used clothing and helmets and not just a little attitude, ask questions, find friends, bikes, events, and gear for your trip.
This worldwide network of motorcycle travelers has regional listings and forums that will help you connect with local riders, riders who have toured the area, and listings of their great Horizons Unlimited Travelers Meetings. This is probably the most reliable place to get information about world travel by motorcycle. They also sell a series of inspirational DVDs. You could spend hours here.
Adventure Rider Forum
ADVRider is wildly popular with motorcyclists everywhere, for their photos, trip reports, and not a little attitude. It's fun and can be useful to travelers.
List of Bay Area Motorcycle Clubs
There are too many to count and keep track of, but Pashnit tries. Here you go.