Take 101 North to the Civic Center exit, and turn on to North San Pedro Road East. Just keep driving straight from there. North San Pedro runs straight into China Camp. The drive is beautiful on a sunny day, and the road is long and winding. Mountain Bikes Yep.
Many trails permit horses, so look out for dung.
Be careful of poison oak. You'll see plenty of signs. The best place to park is just off the road, to avoid a possible parking fee, and to shorten your distance to the trail. Check out the museum that chronicles the Chinese settlement that existed here in the 19th century. For a bite after the hike stop at Whole Foods in San Rafael on N. San Pedro Road on your way out.