Lean Horse Ultra
Custer, United States • 31-1 Jul-Aug 2026
Event
The Lean Horse Ultra Marathon is held in August each year on the George S. Mickelson Trail in the Black Hills of South Dakota. The race was first run in 2005 and is hosted by the town of Custer. It includes multiple distance options and relay formats.
- 100 Mile
- 100 Mile Relay (up to 5 runners)
- 50 Mile
- 30 Mile
- 20 Mile
- 30 Mile Black Hills CrossFit Edition (Singles, team of 3, team of 6)
Course and conditions
The trail surface is crushed limestone and follows an old railroad bed, which produces extended gentle climbs along the route. Average August daytime temperatures at the event are listed as a high of 79 degrees and a low of 53 degrees.
The event is noted as a sanctioned 100-mile race in the United States and is described as a non-technical, scenic rails-to-trails course. Visit the organization's website for the most recent information.