Stephens state park is a good intermediate trail system that is maintained by jorba. The system has good single track mixed with some double track, and there is enough mileage to make a day out of a trip here. Parts of the trail are hilly and rocky, while others are flowy and smooth. The trails do drain well.
Off of route 46 past Hackettstown Medical Center on Willow Grove Street.
http://www.singletracks.com/item.php?c=1&i=7825