Underdown Trail Races
Merrill, United States • 15 Aug 2026
Event overview
The Underdown Trail Races are scheduled for August 2026 in Merrill, WI. The running event on the Underdown Trail system includes these distances:
- 60k
- Marathon
- Half marathon
The mountain bike event, called Thunderdown in the Underdown, includes 111 mile, 37 mile, and 16 mile courses. Each running distance is limited in entry to maintain a smaller field. Proceeds from the event are used to build and maintain trails. Finishers receive a custom commemorative Underdown mug and divisional awards. Race photo digital downloads are available. An after-race party includes live music, food, and beer. The mountain bike race is part of the Wisconsin Endurance Mountain Biking Series (WEMS).
Course and logistics
The course is on the Underdown Trail system and is primarily backcountry singletrack. The route features dozens of boardwalks and passes isolated lakes on terrain shaped by glaciers. The organizers describe steep climbs on singletrack and note that parts of the course go through remote areas. Cell phone service can be spotty. The event provides stocked aid stations and drop-bag transport. A racer guide is provided; the 2024 guide is available for reference until the 2025 guide is released. Visit the organization's website for the most recent information.