The course
The Castle Peak 100K ran a high loop through the Castle Peak and Donner Summit country of the Tahoe National Forest, near Truckee and Soda Springs. It was roughly 95 percent demanding singletrack, with over 16,000 feet of climbing across about 100K (close to 62.4 miles), an average elevation near 7,300 feet, and a high point around 8,900 feet. A few aid stations sat deep in the back country where volunteers hiked the supplies in, because no vehicle could get to them.
Almost all singletrack, almost all up or down
What sets this course apart is how little of it is smooth or flat. With roughly 95 percent singletrack and over 16,000 feet of gain packed into a 100K, you are almost always climbing or descending on trail that wants your full attention. That is a lot of vert for the distance, and it means your legs never get the break that runnable fire road or pavement would hand you on some other race.
So the takeaway for training a course like this is pretty simple. Train the way you will race. Steep, technical, singletrack vert is the most race-specific work you can do, way more than flat mileage. Being efficient power-hiking the climbs and keeping your feet under you on the descents matters just as much as raw fitness out here.
Run high, the whole way
This is not one of those courses with a single big alpine spike and a lot of easy low running. The average elevation sits near 7,300 feet, with the high point close to 8,900 feet, so you spend the whole day in thin air. If you are coming from sea level, every climb feels harder and you recover slower between efforts than the same grade would let you back home.
That is why pacing by effort, not by your flatland pace numbers, is not optional here. The early miles feel easy on fresh legs, and that is the trap. Pushing the pace high and early is exactly how people end up walking the back half.
Remote aid and Sierra mountain conditions
Some of these aid stations were real back-country stations, food and water carried in on foot, so being able to take care of yourself between them mattered. The race ran in the mountain summer window of mid-to-late August, which in the high Sierra usually means warm, dry, exposed afternoons up high and cooler temps at the start and once the sun drops. The sun on the open ridgelines and the dry air drove real fluid and sodium needs, even up at elevation.
So plan to carry enough fluid and calories to cover the long gaps between aid, stay on top of sun and heat through the exposed midday hours, and remember that mountain weather at altitude can turn on you. Those same habits carry over to any high Sierra ultra you train for off this guide.
Aid stations and cutoffs
The course had a series of fully stocked aid stations run by experienced ultra volunteers, with some of the remote ones resupplied on foot. The overall time limit was around 22 hours back when it ran, with intermediate cutoffs at checkpoints along the way, including an evening cutoff people reported at Van Norden.
The climbing and altitude slow almost everyone down late, so the winning move was to bank time against the early and middle cutoffs instead of betting on a fast finish. If you are training for a comparable Sierra 100K, pull that race current cutoff chart and build your pacing plan backward from it, with a buffer.
Pacing strategy for a high Sierra 100K
A vertical, high-altitude, almost-all-singletrack 100K rewards patience and punishes ego. Pace this kind of course by effort and by grade, not by the flat-ground numbers off your home training runs.
Pace the climbs by grade, not by clock
On a course with over 16,000 feet of gain, your moving pace is going to swing all over the place between the climbs and the runnable bits, and that is fine, that is how it should be. Power-hike the steep singletrack efficiently and run the gentler grades. Trying to hold one steady minutes-per-mile number across this terrain is a quick way to cook the climbs and leave nothing for the technical descents.
Use our free grade-adjusted pace calculator to turn your flat fitness into honest effort targets for steep mountain climbs, so you actually know whether you are pacing the vertical sustainably or burning matches you are going to want in the final third.
Set a vert-aware finish goal
A flat-course time prediction is going to lie to you on a course this steep and this high. To set a goal that actually accounts for the vertical, use our vert-aware race time calculator. It works the climbing into your projected finish so you are not stuck on a flat-course estimate that the Sierra will quietly tear apart.
Then check that goal against your recent fitness. Our race equivalent calculator lets you reality-check a 100K mountain target off a recent shorter race, so your plan starts from honest numbers and not wishful thinking.
Respect the altitude
With an average elevation near 7,300 feet and a high point close to 8,900 feet, the whole day happens in thin air. The early climbs are going to feel harder than the same grade at sea level, and pushing them is the classic mistake. Pace the high sections easy by breathing and effort, especially in the first half.
If you can swing it, show up a few days early to adjust, or build some altitude or hill-specific work into your block. Even a little acclimatization and a lot of grade-specific climbing pays off on a course that never drops out of the high country.
Fueling strategy for the mountain conditions
A long, high, exposed mountain effort makes fueling and hydration matter as much as fitness. Altitude kills your appetite right when your engine needs the most fuel, so plan around that.
Carbs: ramp to the high end, on a trained gut
For an effort this long, aim for roughly 60 to 90 grams of carbohydrate per hour, leaning toward the high end once your gut can take it. Use a glucose-plus-fructose blend so you can absorb more than a single sugar lets you, and rehearse your exact hourly carb number on long climbing runs so that 80 to 90 g per hour feels normal by race day, not like some experiment.
Altitude makes all of this harder, because it kills your appetite and slows your digestion. That is one more reason to practice fueling on big-vert runs and to keep eating even when you are not hungry, especially through the high, exposed middle hours.
Sodium and fluid: built for dry exposure
Out on the exposed high ridgelines, dry August air and sun pull real sweat off you even up at altitude, so bias your sodium toward roughly 500 to 800 mg per liter of fluid and bump it up if you are a salty or heavy sweater. Carry enough to cover the long gaps between back-country aid stations. Cramping, a sloshy stomach, that wrung-out feeling late in the race, that is almost always a fluid and sodium problem, not a fitness problem.
Dial in a plan with our free ultra fueling calculator. Put in your weight, your goal time, and the conditions you expect, and it hands you a carb, sodium, fluid, and caffeine prescription per hour built for the duration and the mountain environment. Then go test it on your long runs.
This guide is for planning and training, and it reflects publicly available information about the Castle Peak 100K, which the Donner Party Mountain Runners ran from 2015 through its final edition on August 14, 2021 before ending it. Race details, including status, course, aid stations, and cutoffs, can change, and the numbers here describe the race as it was run. Always confirm current details with the organizer before you train or travel for any event.