To get there:

Take 101 N to Geyserville (about 20min north of Santa Rosa), take the Canyon Rd exit and turn left (go under the free way). Take Canyon rd until it ends at a T with Dry Creek Rd, and go right onto Dry Creek Rd. Follow this until it reaches the Lake Sonoma Recreation Area. This involves a sharp left turn, over the spillway bridge, at the entry to the park. Drive through the lower park area, and up the hill. Continue on this road, past the Skaggs Spring turn off, onto Rockpile Rd. Follow Rockpile Rd, over the bridge across the lake, and go up the hill after the bridge. Look for Grey Pine Flat turnout, on the right, if no one is there, continue on to Lone Rock Flat about 1mi further on (on the right also). Lone Rock is the preferred site, as it has better elevation and horizons, but is sometimes booked by equestrians. For a map, see: http://www.darkhorizons.org/sites/sonoma_road_map1.htm