Race Overview
The Bighorn 100 Mile Endurance Run is an iconic, notoriously tough mountain ultramarathon held every June in the wilderness of Wyoming’s Bighorn National Forest. Established in 1993 to help protect the region from development, this out-and-back course features remote, technical singletrack, wild river canyons, and over 20,500 feet of elevation gain and descent. What makes Bighorn truly unique are its 76 miles of technical trail, unpredictable weather (heat, storms, hypothermia, mud), breathtaking alpine scenery, and the friendly, small-town vibe runners experience at the finish in Dayton. This race is widely regarded as one of the most challenging 100-milers in the country, perfect for ultrarunners craving wild, self-reliant mountain adventure and a true test of grit.
How to Qualify & Enter
The Bighorn 100 is a first-come, first-served event (not a lottery). Registration for the 2026 race opens October 15, 2025 (6AM Mountain). Runners must have finished a recent challenging ultra or have equivalent mountain training. Entries are managed through ItsYourRace (not UltraSignup). There is often a waitlist after the field fills, and there are no refunds after March 31. All rules and qualifier info are available on the official race website.
Course Layout
Runners face a 100.5-mile out-and-back route with approximately 20,500 feet of ascent and 20,750 feet of descent. The course consists of 76 miles of singletrack, 16 miles of rugged jeep road, and 8 miles of gravel. Major climbs begin in Tongue River Canyon and lead to Horse Creek Ridge, with the turnaround at Jaws Trailhead (mile 48). Key features include Dry Fork Ridge, Sally’s Footbridge, wildflower meadows, heavy mud in wet years, and multiple river crossings. The Bighorn course is well marked, but its remoteness and variable conditions demand detailed planning and real mountain experience. Official course maps, elevation profiles, and GPX downloads are available at bighorntrailrun.com.
Field Size
The 100-mile field usually consists of several hundred runners. Final participant and finisher numbers vary due to the demanding course and cutoffs, with drop rates that can spike in bad weather years. Bighorn typically sees 100–200 finishers out of roughly 250–300 starters, with a 35-hour time limit.
Rules
Crews are only allowed at designated locations (start/finish, Dry Fork, Sally’s Footbridge, Jaws). Pacers are permitted from Sally’s Footbridge outbound (mile 30) or inbound (mile 66). Bighorn is a cupless race—runners must bring a reusable cup—and must carry headlamp/lighting for night sections plus recommended weather and safety gear. Strict cutoffs are enforced at all major aid stations. No headphones are allowed, and no refunds or entry transfers permitted.
Aid Stations
There are more than a dozen aid stations, ranging from full-service to water-only. Legendary volunteer crews provide snacks, soups, fruit, hydration, and medical help—even at remote and 4×4-accessed spots like Sally’s Footbridge. The major stops are Dry Fork, Sally’s Footbridge, and Jaws (the turnaround). Note: Crew support at some locations requires high-clearance vehicles. Drop bag service is available at strategic stations.
Winners
Most recent champions (men/women/top times):
2023: Jeff Browning (19:47:19) / Amanda Sullivan (26:01:02)
2022: Shane Rominger (21:35:56) / Amanda Sullivan (24:25:40)
2021: Tyler Fox (18:48:04) / Maria Sylte (25:32:15)
2019: Seth Swanson (19:30:00) / Jessi Morton-Langehaug (26:59:00)
2018: Gabe Joyes (22:34:00) / Yvonne Naughton (27:44:14)
Official Website & Contact Info
Website: bighorntrailrun.com
Email: racedirector@bighorntrailrun.com
Phone: (307) 673-7500
Social: Facebook (Bighorn Trail Run), Twitter/Instagram via official site links
Event location: Dayton, Wyoming