Underdown Trail Races
Merrill, United States • 15 Aug 2026
Underdown Trail Races
The Underdown Trail Races are grassroots trail runs and mountain bike races held on August 15, 2026, at the Underdown Trail system in Merrill, Wisconsin. The running events include a 60k, marathon, and half marathon. The mountain bike event, called Thunderdown in the Underdown, includes distances of 111 mile, 37 mile, and 16 mile and is part of the Wisconsin Endurance Mountain Biking Series (WEMS).
The course uses backcountry singletrack trails formed from glacial activity. The terrain is challenging and remote, featuring many hills and dozens of boardwalks that pass by isolated lakes. Participants should note that cell phone service is spotty in the area.
Proceeds from the event go toward building and maintaining trails at the Underdown. Finishers receive a custom commemorative mug. The event concludes with an after-race party featuring live music, food, and beer. Visit the organization's website for the most recent information.