<b>Update 7/24/14:</b>
There has been about a mile or two added to the upper loop. It's pretty twisty and has some very steep switchbacks. It has the most relief of any trail in Mid-TN.
Interstate 40 to Carthaige. Exit and go north. Take a right on state route 25. 25 ends at 859. Turn right. Go 2 miles and turn right into the campground and boat dock area. The trailhead is in the corner of the first parking lot on your right.
http://www.singletracks.com/item.php?c=1&i=451