The course
The AC100 runs through the San Gabriel Mountains in the Angeles National Forest, stringing together Pacific Crest Trail singletrack, the Silver Moccasin and Gabrielino trails, and stretches of fire road. It just keeps going up and down. Roughly 21,000 feet of cumulative climbing and even more total descent across about 100.8 miles, with the high point near 9,400 feet on Mount Baden-Powell.
The early climb sets the tone
The race starts in the dark at 5:00 AM, and a long, sustained climb comes early, carrying you up toward Mount Baden-Powell, the highest point on the course at about 9,399 feet, on Pacific Crest Trail singletrack. You gain serious altitude in the first quarter of the race while your legs still feel great, and that is the trap. It feels easy to push here, and pushing here is how people blow up at mile 70.
So climb this opening by effort. Hike the steep pitches with purpose and save your running legs for the runnable stuff that comes after. The thin air up high already makes a given grade feel harder than it would at sea level, so do not go chasing a pace number on the first big climb.
Ridgelines, exposure, and the heat
After the early high country, the route spends long stretches on exposed ridgelines and crest trail with almost no shade. This is where the Southern California sun gets you. By late morning and through the afternoon, the open sections can get genuinely hot, and heat is the number one reason runners fade or miss cutoffs out here.
These exposed segments are also where your hydration and sodium have to be on point. Carry enough fluid to cover the long gaps between aid, keep your electrolytes up, and work on cooling your body down with whatever the aid stations have. Treat the hottest hours as survival, just keep moving and stay in the race. Then run again once the sun drops.
Where the race is won or lost
The climbs are not what get you. The descents are. The total descent is bigger than the total gain, and those long, often technical downhills shred quads that have not trained for them. Runners who trash their legs bombing the early descents pay for it in the back half, where every remaining downhill turns into a grind. Quad-specific downhill training is some of the most race-specific work you can do for this course, honestly.
The other thing that decides your race is the night. You will run a full night out, on technical trail, often alone or with a pacer, after many hours of climbing and heat. Staying on top of your fuel and keeping your head in it through the dark, low hours is what separates finishers from DNFs. Keep some margin against the intermediate cutoffs so the night does not catch you behind the clock.
Aid stations and cutoffs
The course has a series of aid stations with water, electrolyte fluids, food, and medical aid, and you can drop bags at the major checkpoints. The overall time limit is 33 hours, a 5:00 AM Saturday start to a 2:00 PM Sunday finish, which is roughly a 19:39 per mile average across everything.
Several early checkpoints have firm cutoffs, so you cannot just stroll the front half. Check the official AC100 checkpoint cutoff chart for the current edition and build your pacing plan backward from those times, with a buffer. The climbing, the heat, and the night all team up to slow you down late, so give yourself room.
Pacing strategy for the AC100
A climbing-heavy, hot, high-altitude 100 miler rewards patience and punishes ego. Pace this course by effort and by grade, not by the flat-ground numbers from your home training runs. The course does not care what your road pace is.
Pace the climbs by grade, not by clock
On a course with roughly 21,000 feet of gain, your moving pace is going to swing all over the place between the climbs and the runnable sections, and that is fine, that is how it should look. Power-hike the steep pitches efficiently and run the gentler grades. Trying to hold one steady minutes-per-mile number across this terrain is a fast way to cook the climbs and have nothing left for the descents.
Use our free grade-adjusted pace calculator to turn your flat fitness into honest effort targets for the steep AC100 climbs, so you actually know whether you are pacing the vertical in a way you can hold, or burning matches you are going to want at mile 80.
Protect your quads for the descents
Because the course loses even more than it climbs, the downhills are the part that sneaks up on you. Hold back on the early descents, run them controlled and light instead of letting gravity hammer your legs, and your back half will be so much better. The runners who finish strong are usually the ones who still have working quads at mile 70.
To set a finish goal that actually accounts for all that vertical, use our vert-aware race time calculator. It folds the climbing into your projected finish so you are not stuck on a flat-course estimate that the San Gabriel Mountains are quietly going to wreck.
Respect the altitude and the night
The high point near 9,400 feet and all the time you spend on the crest mean the early climbs feel harder than the same grade does at sea level. Pace the high sections easy, go by your breathing and your effort. Then plan for the night. As the sun drops, your pace can come back, but only if you stayed disciplined through the hot middle hours and kept eating.
If you want to know how your fitness from a recent race carries over to a 100 mile mountain effort like this, our race equivalent calculator helps you reality-check your goal before you lock in a finish time.
Fueling strategy for the AC100
A hot, exposed, all-day-and-night effort makes fueling and hydration just as important as fitness. The heat on the crest is the thing that wrecks most well-trained runners, so plan for it.
Carbs: ramp to the high end, on a trained gut
For an effort this long, target roughly 60 to 90 grams of carbohydrate per hour, leaning toward the high end once your gut can handle it. Use a glucose-plus-fructose blend so you can absorb more than one sugar lets you, and rehearse your exact hourly carb number on long training runs so 80 to 90 g/h feels normal by race day, not like an experiment.
The heat makes all of this harder, because a hot stomach takes in less. That is one more reason to practice fueling in race-like heat and to keep eating through the hot hours, when your appetite drops off but your body still needs the fuel.
Sodium and fluid: built for the heat
On the exposed San Gabriel ridgelines you can sweat out a lot, so push your sodium toward 500 to 700 mg per liter of fluid and carry enough to cover the long, hot gaps between aid stations. Cramping, a sloshy stomach, and that wrung-out feeling late in the race are usually fluid and sodium problems, not fitness problems.
Build a personalized plan with our free ultra fueling calculator. Enter your weight, your goal time, and the expected heat, and it gives you a carb, sodium, fluid, and caffeine number per hour built for the AC100 duration and conditions. Then go test it in training.
This guide is for planning and training, and it reflects publicly available information about the Angeles Crest 100. Race details, including the date, course, aid stations, and cutoffs, can change year to year, and the 2026 edition uses a rerouted course. Always confirm the current specifics on the official AC100 race website before you train or travel.