⏵ Course guide · Texas Hill Country trail race
Tejas Trails brings a marathon, half marathon, and 10K to Purgatory Creek Natural Area right in the middle of San Marcos, a 13.1 mile single-track loop that feels like the backcountry despite sitting in town. I will walk you through the course first, then give you a pacing and fueling plan for a fast, rolling loop, plus free tools to dial in your own numbers.
These facts come from the official Tejas Trails race page and the RunSignup event listing. Check the current year details, cutoffs, and aid stations before you commit. Race logistics change year to year.
Every distance shares the same 13.1 mile loop through Purgatory Creek Natural Area. The half marathon runs it once, the marathon twice, and the 10K turns around at the first aid station before retracing its steps back to the finish.
The loop mixes fast, flowing single track with wider speedy sections and some genuinely challenging rocky limestone stretches. The terrain rolls rather than climbs, so this is a course that rewards efficient footwork through the technical sections more than raw hill strength. A slight downhill run into the finish line gives you one last chance to close a gap if you have anything left.
Because the marathon repeats the exact same 13.1 mile loop, you get a real data point after your first lap: an honest read on your pace, your fueling, and how the technical sections are treating your legs. Use that first loop to calibrate, not to chase a fast split. Runners who push the limestone sections too hard on loop one often find their footing gets sloppy and slow on loop two.
There are three on-course aid stations, including the start/finish, with water and sports drink at minimum and grab-and-go snacks, fruit, and drinks at the busier stops. The race is cupless, so bring your own bottle or a collapsible cup. Pacers are not allowed, so if you want company on course, register a training partner for the same distance rather than planning on a bib-free pacer joining you late in the race.
The marathon's 10 hour window from a 7:30 AM start gives most trained runners real margin, but the rocky limestone sections punish anyone running purely on flat-ground pace expectations.
A grade-adjusted pace target accounts for the rolling terrain, but the technical limestone sections cost you time in a way pure elevation numbers do not capture. Build in a buffer for those stretches rather than assuming you will hold road-marathon pace once you are past the climbs.
For marathon runners, the repeated loop means you know exactly what loop two has in store after finishing loop one. A vert-aware finish prediction built off your actual first-loop split is a far more honest guide than a flat marathon PR, especially through the rocky sections you will now know are coming.
⏵ Free tools to pace this course
Late January in San Marcos typically starts cool and warms up through the morning, so plan your fueling and sodium to shift as the marathon field works its way through the second loop.
Aim for roughly 60 to 90 grams of carbohydrate per hour across the marathon and half marathon distances. With three on-course aid stations and a cupless format, plan to carry what you need between stops rather than relying entirely on aid.
Start toward 300 to 500 mg of sodium per liter in the cool early miles, and push toward 500 to 700 mg per liter if the day heats up by your second loop. San Marcos in late January is usually mild, but a warm afternoon is not out of the question in Central Texas.
⏵ Build your fueling plan
Get a carb, sodium, fluid, and caffeine plan per hour built for your weight and your goal time 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 and this exact rolling, technical loop. Summit Line reads your real training, builds a plan for repeated terrain like this, and rehearses your fueling so race day is something you execute, not guess at.
It is a genuinely fun, runnable course rather than a mountain test. The 13.1 mile loop through Purgatory Creek Natural Area mixes fast single track with rolling hills and a few rocky limestone sections, and the marathon simply repeats that loop twice. The main challenges are the technical footing in the limestone sections and pacing evenly across two identical loops, not elevation. A 10 hour cutoff on the marathon gives most trained runners real room to finish.
The race runs a 13.1 mile single-track loop through Purgatory Creek Natural Area, right in the middle of San Marcos but feeling like the backcountry once you are on the trail. Expect single track, wider speedy sections, and some challenging rocky limestone stretches, with a slight downhill run into the finish. The half and marathon both use this same loop, the marathon covering it twice, and the 10K turns around at the first aid station (Dreamers) before heading back.
Late January in San Marcos usually runs cool at the 7:30 AM start, warming through the morning as the marathon field works through its second loop. Aim for roughly 60 to 90 grams of carbohydrate per hour on the longer distances, and sodium in the 300 to 700 mg per liter range depending on how warm the day turns. The race is cupless, so bring your own bottle or collapsible cup, and use the three on-course aid stations, including the start/finish, to stay on schedule rather than carrying everything yourself. Build your numbers with the free ultra fueling calculator before race day.
The course closes at 5:30 PM for every distance. Since the marathon starts at 7:30 AM, that works out to a 10 hour window. The half marathon starts at 8:00 AM for a 9.5 hour window, and the 10K starts at 8:30 AM for 9 hours. There are also aid station cutoffs on course, published on the official race site, so check those against your own pace plan before you commit to a goal time.
No. Tejas Trails does not allow pacers at this event, so plan your race as a solo effort or with a training partner registered and running the same distance as you, not as a bib-free companion joining you on course.
Yes, this is one of the more approachable trail marathons on the Tejas Trails calendar. The loop format means you pass through the start/finish area often, the terrain is rolling rather than mountainous, and the aid support is frequent. If you have some single-track experience and can handle rocky limestone footing without losing your rhythm, the 10 hour cutoff and cool January weather make this a solid first trail marathon.
Link this guide
Race directors and clubs: link or embed this guide anywhere. It stays current.
<a href="https://runsummitline.com/guides/great-springs-san-marcos">The Great Springs Trail Race - San Marcos course guide</a>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.