So I just got home from work and was reading this thread. Yes it seems fastdogs did one of the more challenging trails at Castlewood. Singletrackmind described the river trail best - continue down the road and begin the trail right under the train tressel.

fastdogs - I really think you should look at the Team Revolution site. We've been posting about rides at Castlewood each week. We were there just yesterday am. It's definitely much more enjoyable riding with others. You can learn from watching them and the encouragement is rewarding.
http://stlrevolution.com/teamrev/

Also you can always call me at the Alpine Shop (ask for Traci). I have weird hours so I get rides during the week that others might not be able to make.