⏵ Course guide · Arizona Halloween night race
Jackass Night Trail is Javelina Jundred's 31K costumed sibling, a single evening lap of the Pemberton Trail terrain at McDowell Mountain Regional Park run Halloween night. The trail is honest rolling desert, and the atmosphere, party energy, costumes, a festive crowd, is as much the point as the running. I will walk you through the terrain first, then give you a pacing and fueling plan built for a Halloween-night race, with free calculators along the way to dial in your own numbers.
These facts come from the official Javelina Jundred event page, which hosts the Jackass 31K. Check the current date, exact wave start times, and cutoff in the race-day details before you commit. Race logistics change year to year.
Jackass runs a single 31K loop on the same trail network that hosts Javelina Jundred's headline 100 miler, out through Shallmo Wash and Pemberton Wash before curving back toward the Javelina Jeadquarters start/finish. Expect gentle hills, sandy terrain, and short elevation changes rather than any defining climb.
Unlike most of Aravaipa's Insomniac night series, Jackass is one straightforward 31K lap rather than a repeated shorter loop. That means less familiarity with the trail as you go, so pay closer attention on your one pass through technical or wash-crossing sections than you would on a course you get to learn lap by lap.
Jackass runs as part of Javelina Jundred's costumed "Jalloween weekend," one of the most festive events on the ultra calendar. Expect a crowded, high-energy start/finish area, costumes on course, and a generally social tone. If you are chasing a fast time, know that going in; if you are there for the experience, lean into it.
Because Jackass uses part of the same Pemberton Trail system as Javelina Jundred's 100-mile loops, the footing is well established and well marked: gentle rolling hills, sandy washes, and boulder formations typical of McDowell Mountain's high Sonoran desert. None of it is technical in the mountain sense, but sand and wash crossings still ask for attention at night.
With a generous window to the 2:00 AM cutoff and rolling rather than mountainous terrain, Jackass gives you room to choose your own effort, competitive or social.
Decide ahead of time whether you are racing Jackass or running it for the experience, since the festive atmosphere makes it easy to drift into a slower, social pace without meaning to. If you do want a real effort, use a grade-adjusted pace target for the gentle hills so you are not just running on adrenaline from the start-line energy.
A single-lap 31K with a 2:00 AM cutoff gives you a lot of flexibility, but a finish time estimate still helps you plan the rest of your Jalloween weekend, whether that means catching some of Javelina Jundred's daytime action the next morning or just getting to bed at a reasonable hour.
⏵ Free tools to pace this course
At 31K with rolling terrain and a generous cutoff, this is a lighter fueling lift than most Aravaipa night ultras, but late October evenings in the desert can still run warm early on.
For a single-lap effort in this range, aim for roughly 30 to 60 grams of carbohydrate an hour, adjusted for your own pace and goals. Since this is a single lap without repeated aid, plan what you are carrying before the start rather than counting on multiple passes through a station.
Late October evenings in the Phoenix metro can still be warm at the start before cooling through the night. Sodium in the 300 to 500 mg per liter range covers most runners, and carrying your own fluid matters more here than on a looped course where aid comes around every few miles.
⏵ Build your fueling plan
Get a carb, sodium, fluid, and caffeine plan per hour built for your weight, your goal time, and a Halloween-night desert race 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 McDowell Mountain terrain, and your projected pace. Summit Line reads your real training, builds a plan for desert night racing, and rehearses your fueling so race night is something you execute, not guess at.
Jackass is a single lap of the same rolling Pemberton Trail terrain that Javelina Jundred's 100-mile field runs over and over, so the running itself is honest but not brutal: gentle hills and sandy washes through classic McDowell Mountain desert, with short elevation changes rather than sustained climbs. What makes it distinctive is the setting, a Halloween-night costumed race on the same weekend as one of Arizona's biggest ultra parties, run entirely by headlamp with a generous window to the 2:00 AM cutoff.
Jackass Night Trail is the 31K option built into the same Javelina Jundred event, run the evening of the same "Jalloween weekend" as the daytime 100 Mile and 100K races at McDowell Mountain Regional Park. It shares the venue, some of the same Pemberton Trail terrain, and the costumed, festive atmosphere Javelina Jundred is known for, without the multi-loop distance of the headline 100 miler.
The course draws on the same trail system as Javelina Jundred: rolling single-track through Shallmo Wash and Pemberton Wash, sandy terrain, gentle hills, and short elevation changes in the 20 to 50 foot range rather than any single defining climb. Expect classic Sonoran high-desert footing, washes, and boulder formations, all navigated by headlamp after dark.
The final cutoff is 2:00 AM Sunday, November 1, giving runners a generous window from the evening start. Given the single-loop, 31K distance, that cutoff leaves real margin for most trail runners, even accounting for the dark and a Halloween-night pace that might be more social than competitive.
It fits the spirit of the event. Jackass runs as part of Javelina Jundred's "Jalloween" weekend, one of ultrarunning's most costume-friendly parties, so plan gear that lets you run comfortably in the dark while still joining the theme, breathable, non-restrictive pieces over anything that limits visibility or movement on technical trail.
Yes. The single-loop, 31K distance keeps things simple, the terrain is rolling rather than mountainous, and the 2:00 AM cutoff leaves plenty of room. The main things to prepare are a reliable headlamp with backup power and enough experience or comfort with desert single-track that a Halloween crowd and darkness together do not throw off your footing.
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<a href="https://runsummitline.com/guides/jackass-night-trail">The Jackass Night Trail course guide</a>This guide is independent and for planning only. The course details, dates, distances, cutoffs, and aid 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.