The route Varies. There is sigletrack, fire roads Bmx jumps and sweet Downhill sections. I would not suggest riding alone!! I know lots of people who have sighted Mountain Lions!! Bring lots of water and know where you're going!
<br /><br />
Update: These trails are on private property (Pacific Union College) and as such they are not officially sanctioned for riding outside 2 official races each year (Howell Mountain Challenge and Napa Valley Dirt Classic). Also, please avoid this trail on Saturdays out of respect to the landowners. No trail signs in this remote area, ride with extreme caution at your own risk.
Drive North on highway 29 from Napa, through St. Helena,Turn Right on Deer Park Rd. Go straight through 4 way stop sign continue straight to Angwin through twisty roads, turn right on Cold Springs Rd, go straight through stop sign. The road becomes Los Posadas rd. Trail head is a small dirt parking area.
http://www.singletracks.com/item.php?c=1&i=1208