Local reservoir. It is very low now (Oct \'07) Hard pack near the trees, muddy and slow closer to the water. Some rocky areas made it fun. A good loop of the lake in some slow track, but a good workout. Deep end (north end at the dam) got a little steep and loose, but still a good workout. Good scenery
In Ashburn, Off of Dulles Greenway, take Belmont Ridge Road S less than a mile, you will see a sports park to the right. Park in this lot, you will see the reservoir down the hill. Ride between the 4 fields (2 left, 2 Right) down the hill and you will hit the trees. There is a small single track trail you will see. Go through this 30 yards and you will intersect another single track trail. Take a left and you will see the reservior through the trees, there is another small single track but you can create your own entry. Head down to it and pick a direction to loop.
http://www.singletracks.com/item.php?c=1&i=2350