The North Face Endurance Challenge 50 mile run Washington, DC

The North Face® Endurance Challenge returns to Algonkian Regional Park, Great Falls Park and the Potomac Heritage Trail again in 2009. The course keeps runners on their toes with ever-changing terrain as stage 3 of the North Face Endurance Challenge series. 
http://www2.thenorthface.com/endurancechallenge/races/2009/dc/index.html
The Great Falls sections are highlighted by some intense elevation changes, with steep-but-run-able climbs up to 300 feet. The River Trail covers what is widely held as the marquee section the event: up to three miles of tip-toeing and hopping along bluffs high above the Potomac River. The tedious-but-scenic time it takes to cover this section is more than offset by cruising sections of undulating trail in the river basin.