The only distance AC100 offers. For 2026 it is a 100.8-mile out-and-back beginning and ending at Loma Alta Park in Altadena, with a turnaround at Mount Hillyer, run under a 33-hour cutoff. Trekking poles are permitted for the whole distance. The route uses the Gabrielino Trail and passes through Switzer Picnic Area, Clear Creek, Josephine Peak (an aid station for the first time in 2026), Red Box, Newcomb, Chantry Flats, Mount Wilson, the Mount Lowe Motorway, Sam Merrill, and Millard before returning to Loma Alta Park.
Mountain singletrack and fire road through the San Gabriel Mountains, with one paved stretch between Red Box and Mount Wilson. The course reaches its high point near Mount Hillyer and its low point at Loma Alta Park; heat in the lower canyons and altitude on the high sections both come into play over the 100.8 miles. The outbound and return legs are not identical: only the Newcomb-Shortcut Saddle-Chilao-Mount Hillyer section is retraced in both directions, while the approach out of Loma Alta Park (via Clear Creek, Josephine Peak, and Red Box) and the return into it (via Chantry Flats, Mount Wilson, Sam Merrill, and Millard) are different trails.
The Angeles Crest 100 Mile Endurance Run runs through the San Gabriel Mountains above Los Angeles, one of the first hundred-mile trail races in the country and a Western States 100 qualifier. Wildfire, winter storms, and wilderness designations in the Angeles National Forest have forced the race to change its route again and again since 2020. The 2026 edition is a new out-and-back between Loma Alta Park in Altadena and a turnaround at Mount Hillyer.
AC100 started in 1986 as one of the first five hundred-mile trail races in the country, finishing at the Rose Bowl through 1991, then Johnson Field, and, from 2008 on, Loma Alta Park in Altadena. Fires kept the race from being held in 2002 and 2009, and it moved from September to August starting in 2010. Wilderness expansions along the course forced repeated reroutes through the 2010s, and the Bobcat Fire, together with the COVID-19 pandemic, cancelled the race in 2020 and 2021. The route has changed most years since: an out-and-back to Shortcut Saddle, a finish routed via the Kenyon/Devore Trail bypassing Chantry Flats, and a Wrightwood out-and-back in 2025 after the Bridge and Eaton Fires. Winter-storm damage to Highway 2 closed two more sections in 2026, and for the first time the race starts and finishes at Loma Alta Park itself, out and back to Mount Hillyer.
| Mile | Station | Cutoff | Crew access | Bag | Pacer | Med | To next |
|---|---|---|---|---|---|---|---|
| 0.00 | Loma Alta Park | 5:00am | ● | · | · | ? | 11.20 |
| 11.20 | Clear Creek | 8:30am | ● | · | · | ? | 4.10 |
| 15.30 | Josephine Peak | ? | · | · | · | ? | 9.30 |
| 24.60 | Red Box | 12:25pm | ● | ● | · | ? | 8.60 |
| 33.20 | Newcomb-1 | ? | · | · | · | ? | 9.50 |
| 42.70 | Shortcut-1 | 5:45pm | ● | ● | · | ? | 6.40 |
| 49.10 | Chilao-1 | 8:10pm | ● | ● | ● | ? | 3.70 |
| 52.80 | Mt Hillyer | 9:40pm | · | · | · | ? | 3.70 |
| 56.50 | Chilao-2 | 11:00pm | ● | ● | ● | ? | 6.40 |
| 62.90 | Shortcut-2 | 1:25am | ● | ● | · | ? | 9.50 |
| 72.40 | Newcomb-2 | ? | · | · | · | ? | 6.30 |
| 78.70 | Chantry Flats | 6:20am | ● | ● | ● | ? | 6.10 |
| 84.80 | Mt Wilson | 9:35am | ● | ● | · | ? | 5.70 |
| 90.50 | Sam Merrill | 11:05am | · | ● | · | ? | 6.00 |
| 96.50 | Millard | 12:50pm | · | ● | · | ? | 4.30 |
| 100.80 | Loma Alta Park | 2:00pm | ● | ● | · | ? | ? |
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