There's a little known secret in San Francisco called 'the wiggle'. It's a bike route that avoids many of the steep grades of the city. It'll be a nice welcome back to riding real hills instead of the gentle grades of the east. Here in Brooklyn I have to ride at least 20 miles outside of the city to find anything worthy of being considered a leg burner. For mountain biking the best trails are an hour north of the city. It'll be interesting to go from really technical trails to the relatively buffed out single-track of the Marin Headlands.