FIRST ANNUAL ANGELES CREST 100K & RED BOX MOUNTAIN MARATHON
Welcome to the first annual Angeles Crest 100K and Red Box Mountain Marathon, taking place Saturday, March 20, 2027.
Both races will use trails from the current Angeles Crest 100 Mile “Front Range” course, providing runners with a firsthand preview of the terrain and character of the Angeles Crest 100 Mile Endurance Run.
AC100 HISTORY
The Angeles Crest 100 Mile Endurance Run has been held since 1986 and is one of the original five 100-mile endurance runs in the United States.
Traditionally run point-to-point through the San Gabriel Mountains, the AC100 mile course has evolved in response to fires, trail closures, changing conditions and safety considerations. Through every version, its identity has remained the same: steep climbs, rocky trails, remote backcountry, demanding descents and an extraordinary community of runners, volunteers and trail stewards.
These two new races carry that history forward on the current AC100 Mile Front Range course.
ANGELES CREST 100K
The Angeles Crest 100K will begin and finish in Altadena.
Runners will encounter sustained climbing, technical trail, exposed ridgelines, remote mountain terrain and long descents. Completing this course will require preparation, patience, resilience and respect for the mountains.
This is a true mountain 100K. It will be difficult, and finishing it will mean something.
AC100 SILVER TICKETS
The top three male finishers and top three female finishers in the Angeles Crest 100K will each earn a Silver Ticket into the Angeles Crest 100 Mile Endurance Run.
Six runners will leave the inaugural race with the opportunity to advance from the 100K preview to the complete Angeles Crest 100 Mile experience. Silver Ticket recipients must satisfy all applicable AC100 mile registration and eligibility requirements.
RED BOX MOUNTAIN MARATHON
The first annual Red Box Mountain Marathon will also follow the opening section (26 miles) of the Angeles Crest 100 Mile Front Range course.
Starting in Altadena, runners will travel through the western San Gabriel Mountains toward Switzer, Clear Creek, Josephine and Red Box. The race finishes at Red Box after approximately 26 rugged mountain miles.
Although shorter than the 100K, this is not an easy alternative. The course includes substantial climbing, technical trails and remote mountain terrain. It is an excellent introduction to the Front Range and a challenging step toward longer mountain ultras.
This is a point-to-point race. Transportation details will be included in the official runner instructions.
RACE-DAY SCHEDULE
Saturday, March 20, 2027
Angeles Crest 100K: 5:00 a.m.
Red Box Mountain Marathon: 6:00 a.m.
100K field limit: 250 runners
Mountain Marathon field limit: 100 runners
Final course measurements, elevation profiles, cutoff times, aid-station information, required equipment and transportation plans will be published as race preparations are completed.
MORE THAN A RACE
Training runs, trail work and service to the San Gabriel Mountains have always been important parts of the AC100 experience. These races will continue that tradition by encouraging runners to prepare on the course, support the trail community and give back to the mountains.
Come prepared for a serious mountain challenge and the rare experience of traveling through the San Gabriel Mountains on foot.
Be part of the first year.
REGISTER NOW & SAVE:
Register now to secure your spot and take advantage of early-bird pricing for the inaugural Angeles Crest 100K and Red Box Mountain Marathon.
Stay tuned for major website updates following this weekend’s Angeles Crest 100 Mile Endurance Run, including:
• Exact course details and elevation profiles
• Aid-station locations and information
• Downloadable GPX files
• Cutoff times and race-day logistics
• Sponsors and race partners
Be part of the first year and experience the AC100 Front Range course for yourself.
Red Box Mountain Marathon COURSE MAP & ELEVATION
100K COURSE MAP & ELEVATION PROFILE
WEATHER, SAFETY & EVENT MODIFICATION POLICY
The Angeles Crest 100K and Red Box Mountain Marathon are mountain events and are intended to take place rain or shine when conditions can be managed safely. However, the safety of our runners, volunteers, staff and emergency personnel will always come first.
Extreme weather or other circumstances—including heavy rain, flooding, flash-flood risk, snow, ice, lightning, wildfire, smoke, unsafe air quality, landslides, trail damage, road closures, natural disasters, government or permitting-agency directives, or other conditions beyond the control of race management—may require the event to be modified, postponed or canceled.
In consultation with the appropriate land-management agencies and public-safety officials, race management reserves the right to:
• Delay or change start times
• Modify, reroute or shorten either course
• Change aid-station locations or cutoff times
• Suspend or stop an event already in progress
• Move the event to an alternate date
• Cancel the event if no safe alternative is available
If the event is moved to an alternate date, all registrations will automatically transfer to the new date. A registered runner who cannot participate on the alternate date may request a one-time deferral of their base entry to the following year’s Angeles Crest 100K or Red Box Mountain Marathon.
If extreme conditions prevent the event from taking place and a suitable alternate date cannot be secured, registered runners will receive a one-time deferral of their base entry to the following year’s event.
Cash refunds will not be issued for weather-related modifications, postponements or cancellations. UltraSignup processing fees, donations, merchandise purchases and other optional charges are not refundable or transferable. Deferral instructions and deadlines will be communicated by email if the policy is activated.
By registering, participants acknowledge and accept this policy and understand that mountain weather, trail access and public-safety conditions may change before or during the event.
Event's current local time: 3:42 PM PT
