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⏵ Course guide · California ultra

Diablo Trails Challenge 50K Course Guide

The Diablo Trails Challenge 50K is Brazen Racing’s springtime tour of Mount Diablo, and it has earned a reputation as one of the tougher 50Ks in the Bay Area. You climb out of Diablo Foothills, tag the main summit, then climb again to North Peak before the long run home, so it is a real mountain day with a lot of vert packed into 31 miles. I will walk you through the course first, both peaks and all, then give you a pacing and fueling plan built for the climbing. There are free calculators along the way to dial in your own numbers.

⏵ At a glance

Diablo Trails Challenge 50K quick facts

Date
Saturday, April 4, 2026
Location
Castle Rock Recreation Area, Diablo Foothills Regional Park (1700 Castle Rock Rd), Walnut Creek, East Bay, CA
Distances
50K, Half Marathon, 10K, 5K
Elevation gain
50K: roughly 7,000 to 8,000 ft, over both Mount Diablo summits (Brazen does not publish an official figure)
50K start
6:30 AM
Cutoff
50K: 11 hr overall, with intermittent cutoffs (Curry Point mi 13, Summit mi 16.5, Juniper mi 23.1, Burma mi 27.3)
Qualifier
No Western States, UTMB, or Hardrock qualifier status listed by the race

These facts come from the official Brazen Racing race-info page and UltraSignup. Brazen does not publish an official 50K elevation figure, and dates, cutoffs, and aid stations change year to year, so confirm the current race-day details before you commit.

The course: where Diablo is won and lost

The 50K starts and finishes at Castle Rock in Diablo Foothills Regional Park, low in the canyons, and the day is shaped by two big climbs: up to Mount Diablo’s main summit near mile 16.5, then a drop and a second climb to North Peak. There are six aid stations along the way (Little Pine, Rock City, Curry Point, Summit, Juniper, and Burma), but the gaps over the high ground are long and exposed.

The long climb to the summit

The first big effort is the grind from the foothills all the way up to the main 3,849-foot summit of Mount Diablo. It is a long, steady gain on dirt fire road and trail, and it is exactly where overeager people cook themselves. Be patient on this. Hike the steep pitches with purpose, keep your effort even, and you will roll over the top with legs to spare. Push the early grade because it feels good in the cool morning air and you will pay for it twice over on the back half.

Once you tag the summit the views open up to a huge sweep of California, San Francisco one way and the Sierra the other on a clear day. Soak it in, top off your bottles at the Summit aid, and get your head right, because you are not done climbing.

North Peak: the second climb that breaks people

After the summit you descend, then turn and climb again toward North Peak, and this is the part that quietly decides your race. The final approach gets steep and rocky and can even turn into a bit of a scramble, and you are hitting it with tired legs and a fair amount of vert already in them. If you blew the first climb, North Peak is where it shows. If you paced smart, this is where you start passing people.

Keep your effort honest here, power-hike the steep stuff, and do not let a slow, grindy climb wreck your morale. Everyone is hurting on this section. The runners who keep eating and keep their feet moving are the ones who finish strong.

The descent and the exposed run home

From up high it is a long way back down to Castle Rock, and it is fast if you saved something for it. But miles of descending on rocky, rolling trail beat up your quads, and the late canyon rollers have a way of feeling much bigger than they look on the elevation chart. If your legs are trashed or you never trained the downhills, those last miles turn into a slow shuffle.

Practice controlled, runnable descending before race day so you can actually use the downhill late, when your quads are cooked. And remember the high, open stretches give you almost no shade. By midday in April the summit ridges can be warm and fully exposed even if it was cool and foggy at the start, so do not get caught short on fluid up top.

Pacing strategy for a two-summit 50K

With something like 7,000-plus feet of gain stacked into two big climbs, Diablo is about managing effort, not chasing a flat pace chart. Run the climbs by feel, save your legs for North Peak, and work backward from the cutoffs so you always know your buffer.

Pace the climbs by grade, not by the watch

Your flat-ground pace is meaningless on the climb to the summit or the scramble up North Peak. What matters is grade-adjusted effort, so hold a steady output you can sustain up the grade and hike the steep pitches without feeling like you are giving up time. The classic Diablo mistake is running the first climb too hard because the morning feels easy, then falling apart on North Peak and the run home. Use a grade-adjusted pace to turn your real fitness into honest climbing and descending targets and you will not torch the first half.

Build a vert-aware finish prediction and race the cutoffs

Do not guess your Diablo finish off a road 50K time. The two big climbs, the rocky North Peak approach, and the exposure all add real time. A vert-aware finish prediction that accounts for this course’s climbing gives you a realistic window, and just as important, it lets you work back into the intermittent cutoffs. Know what time you need to clear Curry Point, the Summit, Juniper, and Burma, and you can run the day to your buffer instead of finding out the hard way that you are behind.

⏵ Free tools to pace this course

Fueling strategy for the climbs and the exposure

Most runners are out on the Diablo 50K for somewhere around 6 to 10 hours, climbing hard and spending the middle of the day exposed up high. That makes carbohydrate, sodium, and fluid every bit as important as fitness.

Carbs: steady and trained

For a 6 to 10 hour climbing effort, aim for around 60 to 90 grams of carbohydrate per hour, and only push the higher end if your gut is trained for it. Long climbs and afternoon heat both kill your appetite, so keep your intake steady and easy to get down instead of gambling on big doses late. Practice your exact race-day carb rate on hilly long runs so 80-plus grams an hour feels normal by April, not like an experiment you are running on North Peak.

Sodium and fluid: plan for the exposed high ground

It can start cool and foggy down in the canyons, but the summit and North Peak ridges are warm and fully exposed by midday, so do not underdress your hydration. Lean toward the higher end on sodium when it heats up, often around 500 to 700 milligrams per liter of fluid, and more if you are a heavy or salty sweater. Carry enough to get across the long, shadeless stretches between aid stations instead of rationing to the next one and arriving empty. Weigh yourself before and after a hot long run to find your real sweat rate, then build the plan around your own number.

⏵ Build your fueling plan

Get a carb, sodium, fluid, and caffeine plan per hour built for your weight, your goal time, and the Diablo climbs with the free ultra fueling calculator. Browse the rest of the free running tools at the tools hub.

⏵ Train for it with Summit Line

Get a race-day plan built around YOUR fitness, this exact Diablo course profile, and your projected splits. Summit Line reads your real training, builds a plan for the two big climbs, and rehearses your fueling so race day is something you execute, not guess at.

Start free →Explore the demo

Diablo Trails Challenge 50K FAQ

How hard is the Diablo Trails Challenge 50K?

It is one of the tougher 50Ks in the Bay Area, and the climbing is the reason. You start low in Diablo Foothills, grind all the way up to the main summit of Mount Diablo, then drop and climb again to North Peak before the long way home, and depending on whose track you trust that is somewhere in the range of 7,000 to 8,000 feet of gain over about 31 miles. That is a lot of vert for a 50K. The footing is mostly dirt fire road and single-track and a big chunk of it is runnable, but the back half is where a fast start comes back to bite you. Treat it as a real mountain day, not a fast spring tune-up.

How much climbing is in the Diablo Trails Challenge 50K?

A lot for the distance. Brazen does not post an official elevation number and third-party GPS tracks disagree, landing roughly between 6,100 and 8,100 feet, but most runners talk about it like a 7,000-plus foot day. The two big efforts are the long climb from the foothills up to Mount Diablo’s main summit around mile 16 to 17, then a second climb and a short scramble up to North Peak after that. Add the rolling canyon terrain in between and the gain stacks up fast.

Does the Diablo Trails Challenge 50K go to the summit of Mount Diablo?

Yes, and that is the whole point of the course. The 50K tags the main 3,849-foot summit of Mount Diablo (there is a Summit aid station near mile 16.5) and then, after a descent, climbs again to the rockier North Peak. On a clear day from the top you can see an enormous sweep of California, from San Francisco to the Sierra. Hitting both peaks is what makes this race a genuine East Bay classic and a benefit for Save Mount Diablo.

What are the cutoff times for the Diablo Trails Challenge 50K?

The 50K has an 11-hour overall limit off the 6:30 AM start, plus intermittent cutoffs you have to make along the way. The published checkpoints are Curry Point (about mile 13) at 11:10 AM, the Summit (about mile 16.5) at 12:35 PM, Juniper (about mile 23.1) at 2:55 PM, and Burma (about mile 27.3) at 4:05 PM. So you cannot bank all your time for the end, you have to keep moving through the climbs. Always confirm the current cutoffs in the race-day details before you start, since Brazen tweaks them year to year.

What is the terrain and weather like at the Diablo Trails Challenge?

The course runs on Mount Diablo State Park and regional park dirt, a mix of fire road and single-track, with a fair amount of it runnable when your legs are fresh. Early April in the East Bay is usually green and often loaded with spring wildflowers, which is part of why people love this one. Temps can swing, though: cool and even foggy down low at the 6:30 start, then warm and fully exposed up on the open summit ridges by midday. There is very little shade once you climb out of the canyons, so plan for sun and heat on the high, exposed sections even if it feels mild at the start.

Is the Diablo Trails Challenge 50K a good first 50K?

It can be a great goal race for a well-prepared first-timer, but do not pick it because you think a local 50K will be easy. The vert, the second climb to North Peak when your legs are already tired, and the exposure all ask for specific prep: time spent climbing and descending long hills, and a fueling plan you have actually rehearsed. The good news is the 11-hour limit is generous, so if you respect the climbs and hike the steep stuff early, most committed runners have room to finish. Just go in knowing it is a climber’s 50K, not a flat one.

This guide is independent and for planning only. The course details, dates, cutoffs, and aid stations come from public sources and can change year to year, so confirm the current specifics with the official race before you register or run. The fueling and pacing advice is general and not medical advice.