⏵ Course guide · Deep South December mountain 100
Blood Rock runs two laps of a 50.88-mile loop through Oak Mountain State Park near Birmingham, Alabama, 17,512 feet of climbing on singletrack, built intentionally tough as the counterpart to the organizer's gentler Lake Martin races. I will walk you through the course and the 44-hour cutoff first, then give you a pacing and fueling plan built for a long December night on technical trail, plus free tools to dial in your own numbers.
These facts come from the official Southeastern Trail Runs Blood Rock event page. Course markings, mandatory gear, and logistics can change year to year, so confirm the current details before you register or run.
The 100M covers two laps of a 50.88-mile course through Oak Mountain State Park, starting and finishing at the cabins on Tranquility Lake.
Of the 101.79 total race miles, 92.84 are singletrack, run twice as part of the two-lap structure. Only 7.74 miles run on gravel road, closed to vehicle traffic, and just 1.18 miles on pavement. This is a genuinely technical singletrack race, not a road ultra with trail sections mixed in.
The published elevation gain is 17,512 feet, with an equal figure for loss, meaning the descents demand as much attention and quad strength as the climbs. Spread across two identical laps, you will face the exact same climbing profile twice, once with fresh legs and once well into fatigue.
The same organizer runs a more runner-friendly race elsewhere in Alabama, and Blood Rock is explicitly their intentionally grueling contrast to that easier course. Course marking can shift due to interference some years, so downloading the official GPX file and knowing how to navigate with it is a real part of race preparation here, not an afterthought.
With a generous 44-hour cutoff but genuinely tough terrain, the pacing challenge is balancing a conservative first lap against the reality of December darkness on the second.
Because the two laps are identical, your first-lap split is the most honest predictor you will get for the second. A grade-adjusted pace target for 17,500 feet of singletrack climbing helps you set a number you can genuinely repeat, rather than a number that only works once with fresh legs and daylight.
A Friday 10:00 AM start means you will likely run through at least one full night, possibly two given the 44-hour window. Technical singletrack slows down meaningfully after dark, so build that expectation into your finish-time projection rather than assuming your daylight pace holds after sunset.
⏵ Free tools to pace this course
A Friday morning start with a 44-hour window at Oak Mountain State Park in December means real cold-weather fueling and layering decisions, not just carbohydrate math.
Aim for roughly 60 to 90 grams of carbohydrate per hour, but plan specifically for cold-weather palatability, some gels and chews become unpleasant or hard to manage with cold hands late at night, so test your race nutrition in cold conditions before race day, not for the first time on course.
Keep sodium in the 300 to 700 mg per liter range, and take the mandatory gear list seriously, it exists because Oak Mountain State Park in December can turn genuinely dangerous without proper layering. Pack warm layers you can add and shed as temperatures swing across two nights on course.
⏵ Build your fueling plan
Get a carb, sodium, fluid, and caffeine plan per hour built for your weight, your goal time, and a cold Alabama December night 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 two-lap climbing profile, and your projected splits. Summit Line reads your real training, builds a plan for repeated singletrack climbing across two cold nights, and rehearses your fueling so race day is something you execute, not guess at.
Blood Rock is intentionally grueling by design, the organizer's own contrast to their more runner-friendly Lake Martin race. The 100M covers 101.79 miles with 17,512 feet of gain (and an equal amount of loss), almost entirely on singletrack, 92.84 of the 101.79 miles. A 44-hour cutoff is generous on paper, but December weather at Oak Mountain State Park can add real cold-weather difficulty on top of the climbing.
The race runs on a 50.88-mile loop through Oak Mountain State Park, with the 100M covering it twice. The vast majority of that loop, 92.84 miles across two laps, is singletrack, with 7.74 miles of gravel road (closed to vehicle traffic) and just 1.18 miles of pavement. The start and finish sit at the cabins on Tranquility Lake.
The 100M starts Friday at 10:00 AM with a 44-hour cutoff, giving you until early Sunday morning to finish. That is a genuinely generous window for the roughly 17,500 feet of gain, but December conditions, cold temperatures, possible rain, and long nights, mean the extra time matters, since you should expect to move slower after dark on technical singletrack than you would in daylight.
With a Friday 10:00 AM start and a 44-hour window, expect to run through at least one, possibly two, full nights, in December conditions that can be genuinely cold at Oak Mountain State Park. Aim for roughly 60 to 90 grams of carbohydrate per hour and sodium in the 300 to 700 mg per liter range, and plan warm layers and cold-weather nutrition (foods that stay palatable when you are cold and moving slowly) alongside your standard fueling plan. Build your numbers with the free ultra fueling calculator before race day.
The organizer requires all 100 mile runners to carry certain mandatory gear items for safety, citing the course's potential to turn brutal and dangerous in December conditions. Check the current mandatory gear list on the official Southeastern Trail Runs Blood Rock page well before race weekend, since gear checks are a real part of race-day logistics here, not a formality.
Not really, at least not as an entry-level choice. With 17,512 feet of gain almost entirely on singletrack, a December date that brings genuine cold-weather risk, and an organizer who deliberately built this as the tougher counterpart to their more beginner-friendly Lake Martin race, Blood Rock rewards runners who already have solid singletrack vert and cold-weather ultra experience. If you want a first 100 from the same organizer family, look at their more explicitly beginner-oriented events first.
Link this guide
Race directors and clubs: link or embed this guide anywhere. It stays current.
<a href="https://runsummitline.com/guides/blood-rock-100">The Blood Rock 100 course guide</a><iframe src="https://runsummitline.com/embed/race/blood-rock-100" style="width:100%;max-width:420px;height:180px;border:0;" loading="lazy" title="Blood Rock 100 course guide by Summit Line"></iframe>This guide is independent and for planning only. The course details, dates, cutoffs, and mandatory gear 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.