The Idaho Mountain Trail Ultra Festival 100 Race Guide
The Idaho Mountain Trail Ultra Festival 100 is a premier mountain ultramarathon held each fall in central Idaho’s rugged backcountry. This 100-mile event challenges runners with an alpine loop that begins and ends at Jug Mountain Ranch, offering an unforgettable test of endurance and scenic beauty.
When it is run
The 14th annual IMTUF 100 takes place over the weekend of September 20–21, 2025. Racers gather at Jug Mountain Ranch just south of McCall, Idaho for packet pickup on Friday afternoon and a pre-race briefing. The 100-mile field officially starts at 6:00 AM Mountain Time on Saturday, September 20, and runners must finish by 6:00 PM on Sunday, September 21.
How to qualify or register
Registration opens each January 2nd via the UltraSignup platform. Prospective participants must complete the online registration form, agree to the event waiver, and submit payment before the refund deadline of July 1st. This race serves as a qualifier for both Hardrock 100 and Western States 100, so entrants often bring prior 100-mile experience or comparable mountain ultramarathons to the start line.
Particular challenges
Competitors face relentless climbs, steep descents, and extremely technical trail sections. The course traverses remote alpine terrain where assistance is scarce, and weather can shift rapidly from sun to storms. With miles spent above tree line, runners battle altitude, uneven footing, and stretches of ten or more miles between aid stations. Wildlife encounters including elk bugling and bear sightings add to the immersive wilderness experience.
Course format
IMTUF 100 is a single clockwise loop around the Jug Mountain Ranch area. The route crosses eight major mountain passes and winds through ridges and canyons before returning to the hot springs finish. Each year the direction reverses, but for 2025 the loop is set to run clockwise, maintaining the same rugged routing used in past editions.
Elevation profile
Runners accumulate approximately 22,000 feet of total elevation gain over the 100-mile loop. The lowest point sits near Jug Mountain Ranch at around 5,200 feet, while the highest passes reach close to 8,000 feet. Major climbs include back-to-back ascents over alpine summits, with long, technical descents into deep forested valleys before tackling the next ridge.
Terrain breakdown
The course is dominated by narrow, single-track mountain trails with substantial rocky and root-filled sections that demand careful footing. Rough forest roads and occasional jeep tracks comprise a small fraction of the mileage, with nearly all of the route on natural trail surfaces. The bulk of the terrain—over 90 percent—is true mountain singletrack, punctuated by creek crossings and exposed ridgelines.
Time limit & cutoffs
All 100-mile runners must complete the loop within a strict 36-hour cutoff, finishing no later than 6:00 PM on Sunday. While intermediate aid-station cutoffs are not publicly published, participants are advised to maintain an average pace that safely navigates the eight major passes and long aid-station gaps. Any runner missing the final cutoff will be recorded as a DNF.
Aid Stations
The Idaho Mountain Trail Ultra Festival 100 features eleven fully staffed aid stations spaced roughly eight to twelve miles apart along the 100-mile loop. Runners will find aid at Jug Mountain Ranch (start/finish), Louie Lake Dam (mile 20), South Crest (mile 34), Duck Lake (mile 47), Snowslide (mile 55), Lake Fork #1 (mile 61), Lake Fork #2 (mile 69), Boulder Lakes (mile 82), Goat Aid (mile 90), Upper Payette (mile 94), and the final Jug Ranch return (mile 100). Crew access is permitted at Louie Lake Dam, South Crest, Lake Fork #1, and Boulder Lakes via designated parking areas on maintained forest roads. Drop bags may be placed at South Crest and Lake Fork #2; all other stations provide on-site supplies only.
Mandatory Gear
Every participant must carry their required equipment from start to finish. Mandatory items include a minimum of 1 liter of fluid capacity, a fully charged mobile phone with emergency contacts saved, a whistle, a foil survival blanket, a lightweight waterproof jacket with taped seams, a headlamp with spare batteries, and an emergency food supply of at least 500 calories. Runners must also carry a basic first-aid kit (including blister plasters, tape, and gauze) and wear trail running shoes with a pronounced tread suitable for technical mountain terrain. All gear is subject to random checks at the start area and along the course.
Crew & Pacing
Support crews are welcome at four designated aid stations—Louie Lake Dam, South Crest, Lake Fork #1, and Boulder Lakes—where vehicles may park in marked lots. Crews may hand off supplies within the aid station footprint only; roadside pacing or meeting runners along the trail is prohibited. After mile 50 (Lake Fork #1), pacers may join runners and accompany them on the final 50 miles. Crew vehicles must remain on open public roads and may not drive off-road or follow the course. Any unauthorized crew assistance or vehicle incursions onto the trail will result in disqualification.
Navigation
The course is marked continuously with orange flagging and reflective arrows at least every 0.2 miles. Runners are responsible for staying on the flagged route; off-road shortcuts are not permitted. Carrying a GPS device with the official course file loaded is highly recommended as a backup, though reliance on GPS alone is discouraged. Runners must be familiar with basic map-and-compass skills in case of flagging loss due to weather or wildlife interference.
Finish Rates
Historically, IMTUF 100 maintains a finish rate between 40 percent and 50 percent. In the 2022 running, exactly half of the starters reached the finish line, matching 2020’s 52 percent completion rate. More favorable conditions in 2021 saw a 65 percent finish rate, but overgrown trails and late-season heat have driven DNFs back toward 50 percent in recent years. The demanding climbs and long stretches between aid stations are primary factors in the high attrition.
Special Features
IMTUF’s finish line at Burgdorf Hot Springs offers runners the rare chance to soak immediately after completing 100 miles of rugged trail. The race alternates direction annually; 2025’s loop runs clockwise, and next year the counterclockwise routing will reveal fresh terrain. One aid station is uniquely stock-supported by pack goats, adding a frontier feel to South Crest. Finishers receive a custom leather belt—rather than a traditional buckle—but repeat finishers (two completions) earn a commemorative buckle. Course-record honors stand at 19:22:26 for men by David Ayala and 24:04:05 for women by Rachel Entrekin.
Previous Winners
In 2024, David Ayala secured the men’s title in 19:22:26 while Madison Liechty topped the women’s field at 24:22:28. The 2023 champions were Mark Hammond (21:38:01) and Kaci Lickteig (25:01:30). These times reflect the course’s extreme technical demands and elevation changes.
Official Contact Info
For registration questions and race details, reach out to race directors Jeremy and Brandi Humphrey via email at imtuf@runidaho.org or by phone at (208) 315-4017. Visit the official UltraSignup page for updates and the online waiver. The official website for the Idaho Mountain Trail Ultra Festival is hosted on the Run Idaho portal at runidaho.org/imtuf, where you can find detailed race information, course maps, and contact details. The official signup page is on UltraSignup under event ID 121354 (ultrasignup.com/register.aspx?did=121354), which handles entries, waiver signing, and payment processing.