The Vermont 100 Mile Endurance Run (West Windsor, VT)
The Grand Slam for ultrarunners is four 100-mile races including California's Western States 100, Utah's Wasatch Front 100 Mile Endurance Run, the Leadville Trail 100 in Colorado, and the Vermont 100 Mile Endurance Run (or, simply, "Vermont," among insiders). Vermont is mostly dirt roads and trail, winding its way through small New England towns, farms, and meadows. Part of the race even shares a trail with a 100-mile horse race that occurs simultaneously. Entrants are required to have logged eight hours of volunteer time at other races before applying, which lends to the camaraderie of the race.
More Information: To qualify, you'll need to have completed a 50-mile race in less than 12 hours. [Late July; vermont100.com]