Franklin Falls or 'The Dam' is a NEMBA maintained trail which provides little in the way of technical riding, but has a lot of great, fast, winding single track. Here you'll find quick, short, heart pounding climbs, short downhill sections, roots (not too bad), one very small plank crossing a river (on Whaleback), and a few log obstacles (quite small). There are about ten single trails, but you can mix it up however you like.
My favorite route is starting from the parking lot, take the gravel road through the chain link fence, which will meet up with another gravel road, which you'll follow. THAT will merge with another road, but keep on heading forward, turn right on the next small path, and immediately on your right will be the beginning of Whaleback Trail. Whaleback will criss-cross that small path a few times, but keep going.
Eventually, you will come out on a road that doesn't look well used, and up the hill immediately in front of you begins Middle Trail, which is marked in orange. From here, I like to go to Chicken Ravine, and to do that take the first right (marked with orange), and continue on. Pass the entrance to Bee Trail, and the next one on your left is Chicken Ravine. This is by far my most favorite trail. You can fly down the middle, but where's the fun in that? On either side of the ravine, you'll notice paths of other bikers going up and down the walls of the gully. Do it. At the bottom, you'll come out on the beltline road/service road. Take a left, skip the first trail on your right (marked in red) and take the next trail on your right, which is the Lost Wall Trail. That will take you to the yellow-marked Heritage Trail, which will come out back on the service road. Take a right, and a little ways up on the left continues the Heritage Trail. I usually just take heritage back to the middle trail, and from there I hit Moose Gully back to the gravel road, and then back to the parking lot. Takes me about an hour, and my friend is usually done running by then. I am not the best direction-giver, but here is the link to the map.
Franklin Falls is an excellent place to bike. The ground here soaks up water like nothing else, and I've yet to see a puddle (except on the beltline/service road, near the river when stuff likes to flood during the spring), and attendance is really low, yet the trail seems to be very consistently maintained. One warning: if you're like me and want to ride out onto the dam, at the very end, past the gazebo, where the grassy land ends in something of a point next to the fence, there is an underground yellowjacket nest (as of April 12, 2010). Just be careful.