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⏵ Course guide · Arizona ultra

Colossal Vail 50/50 Course Guide

The Colossal Vail 50/50 is a fast, rolling high-desert trail ultra on the Arizona Trail, staged out of Colossal Cave Mountain Park near Vail, southeast of Tucson. It is one of the more runnable big-distance days you will find out here, which makes it a brilliant first 50 Mile or a real chance at a personal best. I will walk you through the course first, then give you a pacing and fueling plan that fits a runnable, exposed December desert ultra. There are free calculators along the way to dial in your own numbers.

⏵ At a glance

Colossal Vail 50/50 quick facts

Date
Saturday, December 5, 2026 (early December, a long-running AZT classic)
Location
Colossal Cave Mountain Park, Vail, AZ, about 24 miles southeast of Tucson, on the Arizona Trail
Distances
50 Mile · 55K (about 34 mi) · Daytime Half (about 13.6 mi) · Night Half (13.1 mi)
Elevation gain
50 Mile: about 4,000 ft · 55K: about 2,300 ft · Half: about 1,300 ft
Start
50 Mile 7:00 AM · 55K 7:15 AM · Daytime Half 9:00 AM · Night Half 5:00 PM
Cutoff
50 Mile about 15 hr · 55K about 9 hr at the final aid · Night Half about 4.5 hr · Daytime Half no posted limit
Qualifier
No Western States, Hardrock, or UTMB Running Stones status listed by the race

These facts come from the official race site and UltraSignup. Cutoffs and start times vary a little across sources and year to year, so check the current date, cutoffs, and aid stations in the race-day details before you commit.

The course: where Colossal Vail is won and lost

Everything starts and finishes at La Posta Quemada Ranch inside Colossal Cave Mountain Park, around 3,300 to 3,400 feet. The 50 Mile is two out-and-back legs stitched together (a longer south leg and a shorter north leg) on smooth, rolling Arizona Trail single-track, with a high point near 4,200 feet. The 55K and the halves run pieces of the same trail. There is no big climb to fear here. The challenge is that the ground is runnable, so the race is about not letting that lull you into going out too hard.

The south leg: smooth, rolling, and seductively fast

The main out-and-back heads south on the AZT toward Sahuarita Road and the Peaks View turnaround near mile 17, rolling through saguaro forest and desert scrub between Saguaro National Park and the Santa Rita foothills. It is genuinely fast trail, gentle grades, good footing, and that is the trap. Early in a cool morning this stretch feels effortless, and every year people bank time here that they pay back with interest later. Run it like you have a long day ahead, because you do.

Aid comes at Gabe Zimmerman Trailhead near mile 4.9, Sahuarita Road near mile 11, and the Peaks View turnaround near mile 17, so the gaps are reasonable. Even so, the desert is dry and there is almost no shade, so top off fluid and keep eating from the very first aid station rather than waiting until you feel like you need it.

The 50 Mile north leg: the second out-and-back is where it gets real

After the south leg you come back through the ranch and head out on the north leg, with 50-Mile-only aid at La Selvilla and Pistol Hill. This is where a 50 Mile stops being a long fun run and starts asking questions. The terrain is still rolling and runnable, but now it is warmer, the sun is up, and your legs already have a long out-and-back in them. The runnable ground that felt free in the morning quietly turns into work.

This is the part of the day to be disciplined about walking the short rises on purpose, keeping your fuel and fluid going in, and settling into a rhythm you can hold to the finish. Get this leg right and Colossal Vail rewards you with a fast, satisfying close. Get greedy on the south leg and this is where it unravels.

Sun, exposure, and the cold-to-warm swing

Do not let December fool you. The 7:00 AM start can be down in the 40s Fahrenheit and dark, then the day climbs into the low 60s with strong, dry, high-desert sun and very little shade anywhere on course. That swing is the whole weather story. Start with a layer you can stash, and once it warms up treat this like an exposed, sun-baked course: manage fluid, keep sodium going, and do not get caught dehydrated just because the air feels mild.

The footing is forgiving compared to Arizona’s rockier mountain races, so you will not be scrambling. But runnable trail plus real sun plus dry air is its own kind of test over 50 miles, and the people who respect the exposure tend to be the ones still moving well at the end.

Pacing strategy for a fast, runnable ultra

Colossal Vail is one of the rare ultras where your road pace actually means something, because the trail is so runnable. That is a gift and a hazard. The whole game is starting conservatively on the easy early miles so you can still run the back half.

Negative-split the easy ground, do not bank it

Because the south leg is so smooth and the morning is cool, your effort will feel low for the speed you are running, and that is exactly when people overcook the first half. Pick a goal effort you can hold all day and let the early miles feel almost too easy. Walk the short rises even when you do not need to. A grade-adjusted pace keeps you honest on the gentle rollers, where it is easy to drift faster than you should without noticing.

Build a realistic finish prediction and work back to the cutoffs

On runnable trail your finish time is closer to a road equivalent than on a mountain course, but the heat, the dry air, and 4,000 feet of cumulative gentle climbing still add real time over 50 miles. Use a vert-aware finish prediction to set an honest target, then work back into the roughly 15-hour 50 Mile and 9-hour 55K windows so you know the buffer you should have at each aid station. If you are chasing a first finish, planning against the cutoffs early keeps a slow patch from turning into a missed time limit.

⏵ Free tools to pace this course

Fueling strategy for a long day in dry desert air

A 50 Mile here is a long day, often well into double-digit hours, on exposed, dry trail. The 55K is shorter but still a several-hour effort. Carbohydrate, sodium, and fluid carry as much weight as your fitness does, especially once the sun is up.

Carbs: steady, trained, and started early

For a long ultra effort, aim for roughly 60 to 90 grams of carbohydrate per hour, and only reach for the top end if your gut is trained for it. Because the early miles feel so easy, it is tempting to under-fuel at the start, then you fall into a hole on the back half that is hard to climb out of. Start eating at the first aid station and keep it steady. The aid stations here run Tailwind and the usual ultra snacks, but practice your exact race-day carb rate on long runs so race day is just repetition.

Sodium and fluid: respect the dry, exposed air

Dry desert air and full sun pull more water out of you than the mild temperature suggests, so do not ration fluid to the next aid and arrive empty. Keep sodium going in, often somewhere around 500 to 700 milligrams per liter of fluid, and more if you are a heavy or salty sweater. Weigh yourself before and after a long run in similar conditions to find your real sweat rate, then build the plan around your own number instead of a generic guess.

⏵ Build your fueling plan

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

⏵ Train for it with Summit Line

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Colossal Vail 50/50 FAQ

How hard is the Colossal Vail 50/50?

By trail-ultra standards Colossal Vail is on the friendlier end, which is exactly why people love it. The 50 Mile has roughly 4,000 feet of climbing spread over fast, rolling Arizona Trail single-track, and the 55K is more like 2,300 feet, so there is no soul-crushing mountain pass anywhere. What makes it honest is that the terrain is runnable, so you actually have to keep moving to beat the clock, and the December high desert is dry and exposed. It is a great first 50 Mile or a real shot at a personal best, but do not mistake runnable for easy.

How much climbing is in the Colossal Vail 50/50?

The 50 Mile has about 4,000 feet of total gain, the 55K about 2,300 feet, and the daytime half about 1,300 feet, per the official course info. The start sits around 3,300 to 3,400 feet and the high point is near 4,200 feet, so there are no big single climbs, just continuous gentle rolling terrain on the AZT. The 50 Mile gets there by stacking two out-and-back legs (a south leg and a north leg), which is why its gain is roughly double the 55K.

What are the cutoff times for the Colossal Vail 50/50?

The official Just the Facts page lists about a 15-hour limit for the 50 Mile (a 7:00 AM start to roughly 10:00 PM), about 9 hours for the 55K measured at the final aid station, and about 4.5 hours for the night half. The daytime half has no posted hard limit. Some third-party calendars quote slightly different numbers, so confirm the current cutoffs and any aid-station time limits in the official race details before you start.

What is the terrain and footing like at Colossal Vail?

This is high-desert Arizona Trail single-track, and it is built for running. Expect smooth to moderately rocky tread through saguaro cactus forest, desert scrub, and the low foothills between Saguaro National Park and the Santa Rita Mountains, with a short dirt-road connector or two near the ranch. It is far less technical than the rocky mountain courses Arizona is known for, so it rewards steady, efficient running rather than scrambling. There is real sun exposure and very little shade, so treat it like an exposed course even in December.

What is the weather like for the Colossal Vail 50/50 in December?

Early-December mornings near Vail and Tucson are cold, often down in the 40s Fahrenheit at the 7:00 AM start, then the day warms into the low 60s with strong, dry desert sun. The swing from a cold dark start to a sunny exposed afternoon is the thing to plan for: layers you can shed, and real sun and hydration management once it heats up. It is usually dry, but the high desert can throw a cold, windy, or wet day, so check the forecast and pack for the start temperature as much as the finish.

Is the Colossal Vail 50/50 a good first 50 Mile?

It is one of the better first-fifty options in the Southwest. The climbing is modest and spread out, the footing is runnable, the out-and-back format means you see the leaders and your friends and you are never far from an aid station, and the roughly 15-hour limit gives a prepared runner real room. The honest catch is that a runnable course gives you fewer built-in walking breaks, so you need the aerobic base to keep shuffling for the back half, plus a rehearsed fueling plan for a long day in dry desert air.

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.