East of Santa Rosa in the Sonoma Valley, the 5,000 acre Annadel State Park has 12 miles of narrow meandering singletrack, along with miles of dirt roads. The trails are well signed and pass through open meadows and oak/fir forests. As Annies Dell used to be an old quarry, the routes can be quite rocky.
To reach the mountain biking trailhead from Santa Rosa off US101, follow SR12 as it eventually turns into Farmers Lane. Turn right onto Montgomery Drive and then turn right on Channel Drive into the park. Follow Channel Drive to the parking lot at the end.
The best singletrack is the the northwestern section of the park. From the parking area, follow the Warren Richardson Trail (an old fireroad) to reach the singletrack trails.
Overall, Annadel State Park is the 26th most popular mountain bike trail of all 132 mountain biking rides in California.