Running since 1986, and one of the most volatile courses in American ultrarunning — fire, drought, and wilderness closures have forced a course change almost every year this decade.
Quick facts
- Location: Loma Alta Park, Altadena, CA (2026: out-and-back start/finish, first time in race history)
- Date: October 3, 2026 — the first October running since 2008, moved from the traditional August date for cooler temperatures
- Distance: 100.2 miles
- Website: ac100.com
- Contact: Ken Hamada, ken.hamada3@gmail.com
- Registration: UltraSignup, lottery-based
Course description
The historic AC100 ran point-to-point from Wrightwood to Altadena through the San Gabriel backcountry. Fire damage and Highway 2 closures have forced a full course change almost every year recently — in 2026, the race runs as an out-and-back from Loma Alta Park in Altadena for the first time in its history, traveling through Clear Creek, Mt. Josephine, Red Box, Newcomb, Shortcut, and Chilao, turning around near Mt. Hillyer before returning via Chantry, Mt. Wilson, and the front-range trails. This is a course that changes based on what the mountains and the fire season allow — always confirm the current-year route on the official race book before relying on any specific segment description.
Elevation change
Roughly 20,000+ feet of gain across the course, ranging from 1,135 to 9,300 feet in elevation. The traditional point-to-point course measured 19,930 feet of gain over 100.2 miles; the 2026 out-and-back configuration is comparable but not identical.
Checkpoints on the 2026 course
Clear Creek, Mt. Josephine, Red Box, Newcomb, Shortcut, Chilao, the turnaround near Mt. Hillyer, then back through Chantry Flats and Mt. Wilson to the finish at Loma Alta Park. See the official 2026 Racebook on ac100.com for exact mileages, cutoffs, and crew access at each station.
Special conditions & average temps
Historically run in August, when canyon temperatures regularly exceed 100°F with no breeze and dry heat that has defined the race for decades — the move to an October date for 2026 is specifically meant to bring cooler conditions and higher finish rates. Even so, expect big day-to-night temperature swings at altitude (the course tops out near 9,300 feet) and long exposed sections with little shade.
Recent results — top 3, men & women
2023 was cancelled; the last three runnings are 2025, 2024, and 2022.
2025
- Men: 1. Max Jolliffe 21:23:43 · 2. Peter Davidson 22:10:35 · 3. Ruperto Romero 22:18:25
- Women: 1. Jian Springer 27:57:05 · 2. Liz Clarke 29:12:55 · 3. Erin Hakim 30:24:11
2024
- Men: 1. Michael Eastburn 18:49:59 · 2. Clark Messman 19:11:18 · 3. Rene Dorantes 19:54:49
- Women: 1. Megan Eckert 22:02:52 · 2. Sarah McMahon 26:25:55 · 3. Yumi Vielpeau 27:49:13
2022
- Men: 1. Wyatt Million 21:09:42 · 2. Michael Eastburn 22:07:44 · 3. Anthony Snitker 23:25:37
- Women: 1. Ashley Hall 25:53:00 · 2. Rosalia Guarischi 27:59:08 · 3. Elizabeth Ochoa 28:42:17
Registration deadline & how to get in
Entry is lottery-based through UltraSignup. For 2026, the lottery opened September 19, 2025 and closed September 29, 2025, with entrants and the waitlist published October 3, 2025 — roughly a full year ahead of race day. Contact Ken Hamada directly for questions about reserving a spot.
Traveling to this race? Find lodging near the venue via Hotels.com.