The Green Rock Trail is a 14.5 mile route (29 miles out-and-back with over 4,000 ft of vert) that connects Rockwoods Range, Greensfelder County Park, and Rockwoods Reservation. This long connector is one of the oldest in the area, dedicated on May 11, 1968 by the Greater St. Louis Area Council of the Boy Scouts of America. The trail showcases several features of Ozark terrain (steep slopes, winding ridge tops, narrow hollows) all less than a hour's drive from downtown STL. The southern terminus is located off of Fox Creek Road and the northern terminus is off of Glencoe Road within Rockwoods Reservation. Out-and-back trips can begin at either terminus, but typically start at Fox Creek. The only year-round, potable water sources are 2 water fountains located in Rockwoods Reservation, one at the visitor center and the other by the privy 0.1 miles from the trailhead.
I don't know why this route hasn't been more popular! I'll be planning on making an unsupported attempt going out and back the weekend of April 18th as long as weather isn't horrible.