Finding this loop is the key to having fun mountain biking at Harbins Park. Exit off the back end of the ridge run loop by jumping on the paved bike trail for a little ways. You'll get off the paved trail by riding over a rock pile and crossing a slickrock stream bed a little ways in. This is the advanced loop, and the singletrack is totally different than everything else at Harbins. It is built better, with bigger climbs and descents, and WAY more flow.
The crowning jewels of the advanced loop are the large granite slick rock section, and the freeride/downhill section filled with tabletops, berms, and kickers. If you find the right trail to ride back up, you can just loop the jumps all day if you'd like. They're awesome! Enjoy this Gwinnett County jem!