Take Highway 29 north from Calistoga, where it
becomes a winding highway climbing up the hills. You will see the sign Robert Louis Stevenson State Park, named after the famous writer who
tried to mine silver here in the 1860's. A few miles past the sign the
road reaches a saddle before descending to Lake County. The hiker's
trailhead (2300 feet) is on the left side of the road at the saddle,
parking area is on the right. Further north for ~500 feet is the
biker's trailhead (2200 feet) which leads directly onto the (gated)
fire road, also on the west side of the road. The distance to North
Peak of Mount St. Helena is about 5.5 miles from either trailhead.
Follow the hiking trail for 1 mile until you come out onto the fire road. Remember the location of the turn off, since the trail sign is somewhat hidden. Go left (up) on the fire road. After reaching the summit plateau there are turn offs that lead to South Peak, Middle Peak, etc. Follow the main road to North Peak.