3 running, cycling, and ultra events in Custer, South Dakota

Registration Closes July 12th 2026!

RACE OVERVIEW

The Lean Horse Ultra Marathon is run in August every year in the Black Hills of South Dakota. It was first run in 2005. It features a 100-mile race, a 50-mile race, a 30-mile race, a 20-mile race, and a 30-mile Black Hills CrossFit Edition - Singles, 3, and 6 person relays. The course is held on the George S. Mickelson Trail.

Course Overview

Surface: Crushed Limestone

Course: Mickelson Trail

Elevation Profile: Extended gentle climbs. This is due to the fact the course is on an old railroad bed.

Hosting Town: Custer, South Dakota

Average August daytime temperature: High of 79 degrees. Low of 53 degrees.

Fun Facts

33rd sanctioned 100-mile race in the United States

Known as one of the best non technical courses in the United States

One of the most scenic rails to trails courses in the country

The Fall Mickelson Trail Trek follows one of the most iconic rail-trails in the country: the George S. Mickelson Trail, winding 109 miles through the very heart of South Dakota’s Black Hills. Inducted into the National Rail-Trail Hall of Fame in 2010, the trail is built on a historic railroad grade and surfaced with smooth crushed limestone, it offers a front-row seat to landscapes you simply can’t see from the highway — quiet pine forests, granite outcroppings, wide open meadows, and hidden mountain valleys.

In autumn, the trail comes alive with golden aspens, deep green pines, and crisp mountain air, making it one of the most beautiful times of year to ride. Wildlife is more active, the crowds are thinner, and every overlook feels like a private postcard.

Along the way, riders pass through four cool, echoing railroad tunnels and roll across more than 100 towering trestle bridges, many of them perched high above creeks, canyons, and forested ravines. Each mile tells a story of the region’s mining past, railroad heritage, and wild beauty, creating a ride that feels as much like a journey through history as it does a cycling adventure.

The trail’s gentle railroad grade makes most of the route comfortably rideable, but the Black Hills still deliver their signature challenge. The climb toward Dumont — including the long, steady stretch from Rochford — rewards riders with sweeping views and a deep sense of accomplishment at the highest point on the trail.

This is more than a bike ride — it’s a chance to experience South Dakota’s most legendary trail at its most spectacular time of year.