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⏵ Course guide · Cave start + Last Person Standing

Great Springs Trail Race - Natural Bridge Caverns Course Guide

Tejas Trails pairs two very different races at Natural Bridge Caverns: fixed 4, 8, and 16 mile runs that start with a stretch inside the cave itself, and a Last Person Standing run and ruck that keeps going, loop after hourly loop, until only one of each is left standing. I will walk you through both formats first, then give you a pacing and fueling plan built for whichever one you are racing. There are free calculators along the way to dial in your own numbers.

⏵ At a glance

Great Springs Natural Bridge Caverns quick facts

Date
Saturday, September 26, 2026, until the Last Person Standing
Location
Natural Bridge Caverns, 26495 Natural Bridge Caverns Rd, San Antonio, TX
Fixed distances
4 mile, 8 mile run & ruck, 16 mile, Youth 1 Mile, all starting inside the cavern
Last Person Standing
Runners: 4.1667 mile loop, every hour on the hour · Ruckers: 2.47 mile loop, every hour on the hour
LPS start
7:00 AM mass start on the surface at the race hub arch
Fixed-distance starts
Staggered by check-in group inside the cave: 7:45 AM first group, 8:45 AM last group
Cutoffs
16 mile final-lap cutoff 11:30 AM · fixed-distance course closes 1:30 PM (open to LPS only after that)
Format
Last Person Standing ends only when one runner and one rucker can no longer complete a lap within 60 minutes

These facts come from the official Tejas Trails event page. Check the current year details, cutoffs, and course map before you commit. Race logistics change year to year.

The format: a cave start, and a race with no finish line

This is really two events sharing one venue: fixed-distance races that start underground, and a Last Person Standing backyard ultra that runs on the surface until attrition, not a clock, decides the winner.

4, 8, and 16 mile: starting inside the cavern

The 4 mile, 8 mile run & ruck, and 16 mile races all begin with roughly a quarter mile inside Natural Bridge Caverns before you emerge onto surface trails over flowing hills and wooded landscape. Runners are assigned to a staggered starting group by their check-in time, so groups of mixed distances go into the cave together, and awards are based on chip time rather than gun time to account for that stagger. After exiting the cave you pass through the race hub and cross a timing mat at the 0.5 mile mark, but you are not finished yet: the course brings you back around to the race hub for your actual finish later.

Last Person Standing: a 4.1667 mile loop, every hour, forever

Runners take on a 4.1667 mile loop, ruckers a 2.47 mile loop, both starting and finishing at the race hub arch on the surface. The race director blows a whistle twice at five minutes before each hour, then once to start the next lap. Finish inside 60 minutes and you can rest, eat, or sleep until the next start; miss the 60-minute window, or fail to be at the line when the whistle blows, and you are eliminated. The event runs until exactly one runner and one rucker remain who can still complete a lap in an hour, with no scheduled finish time at all.

Underground caverns, above-ground adventure

Beyond the race itself, Natural Bridge Caverns offers cave tours and a zip line and ropes course you can use with a discount code from your registration, and the on-site restaurant and snack stands stay open for a real meal after your race, or a quick bite between Last Person Standing laps.

Pacing strategy for a cave start and an hourly loop

The right pacing approach here depends entirely on which race you signed up for; these are two fundamentally different problems.

For the 4, 8, or 16 mile: pace it like any trail race, then respect the cutoff

The staggered cave start means your official time comes from chip time, not gun time, so do not panic about a late group start. What matters is finishing your final lap before the 11:30 AM cutoff on the 16 mile, or reaching the 1:30 PM overall course closure on any distance. A grade-adjusted pace target for the wooded, hilly surface trail keeps you honest after the novelty of the cave section wears off.

For Last Person Standing: your only real decision is effort per lap

Finishing a 4.1667 mile lap in 45 minutes instead of 55 does not help you, it just shrinks your rest window before the next whistle. The winning strategy is almost always the slowest pace that still reliably clears the 60-minute cutoff with a comfortable buffer, since the race rewards whoever can repeat that same effort the most times, not whoever runs any single lap fastest.

⏵ Free tools to pace this race

Fueling strategy for a cave race and a backyard ultra

Late September in the San Antonio area can still run warm during the day, which matters most for anyone logging hour after hour of Last Person Standing loops through the afternoon.

Fixed distances: standard trail race fueling

Aim for roughly 60 to 90 grams of carbohydrate per hour on the 16 mile, scaling down for the 8 and 4 mile distances, and sodium in the 300 to 700 mg per liter range. There is not much time between the cave start and your finish on the shorter distances, so pre-race fueling matters as much as anything you carry.

Last Person Standing: eat every lap, not when you feel hungry

With only a few minutes between finishing a lap and the next hourly whistle, favor real food you can eat fast, sandwiches, potatoes, whatever sits well, over anything requiring prep. Eat and hydrate every single lap on a schedule rather than waiting for hunger, since hunger arriving deep into a Last Person Standing race usually means you are already running a caloric deficit that is hard to climb out of.

⏵ Build your fueling plan

Get a carb, sodium, fluid, and caffeine plan per hour built for your weight, your goal time, and a warm late-September Texas 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, whether you are racing the 16 mile against the clock or the loop against everyone else in Last Person Standing. Summit Line reads your real training, builds a plan for repeatable effort, and rehearses your fueling so race day is something you execute, not guess at.

Start free →Explore the demo

Great Springs Trail Race - Natural Bridge Caverns FAQ

How does the Last Person Standing format work at Natural Bridge Caverns?

Runners take on a 4.1667 mile loop and ruckers a 2.47 mile loop, both starting and finishing at the race hub arch on the surface, once every hour on the hour. Finish your loop inside 60 minutes and you earn the right, and the obligation, to start the next one; the remaining time before the hour is yours to refuel, use the toilet, or even sleep. Miss the cutoff, or fail to reach the start line for the next lap, and you are out. The race does not end until exactly one runner and one rucker are the only ones left who can still finish a lap in an hour.

How hard is the Great Springs Natural Bridge Caverns race?

It depends entirely on which event. The fixed 4 mile, 8 mile run & ruck, and 16 mile races start with a genuinely unique quarter-mile stretch inside Natural Bridge Caverns before emerging onto wooded surface trails, a novelty that adds real logistics (staggered cave-entry groups, chip-time awards) without necessarily adding brutal difficulty. The Last Person Standing format is a different animal entirely: there is no finish line and no mercy, just loop after loop until attrition decides the winner, which can mean many hours or well over a day on your feet depending on the field.

How much climbing is in the Great Springs Natural Bridge Caverns race?

The official race page does not publish a specific elevation gain figure for either the fixed-distance courses or the Last Person Standing loop. What is confirmed is that after exiting the cave, the fixed-distance courses wind through beautiful trails over flowing hills and wooded landscape before returning to the race hub. Check the official course map and GPX for current elevation detail before you build a pacing plan.

How should I fuel for the Great Springs Natural Bridge Caverns race?

For the 4, 8, and 16 mile races, treat it like any single-effort trail race: aim for roughly 60 to 90 grams of carbohydrate per hour on the 16 mile distance, less for the shorter options, and sodium in the 300 to 700 mg per liter range for a late-September Texas day. For Last Person Standing, fueling is a completely different problem: you get a few minutes each hour to eat, so favor food you can grab and eat fast between laps, real food and easily digestible carbohydrate, rather than anything that takes real prep time. Hydrate and eat something every single lap rather than waiting until you feel hungry, since by the time hunger hits deep into a Last Person Standing race, you are already behind. Build your baseline numbers with the free ultra fueling calculator before race day.

What are the cutoff times for the Great Springs Natural Bridge Caverns race?

The 16 mile race has a final-lap cutoff of 11:30 AM, and all of the fixed-distance races (4 mile, 8 mile, 16 mile) close at 1:30 PM, after which the course belongs to Last Person Standing runners and ruckers only. Last Person Standing itself has no fixed cutoff by design: it runs every hour on the hour until only one runner and one rucker remain who can finish a lap within 60 minutes.

What is the terrain and weather like at the Great Springs Natural Bridge Caverns race?

Every distance starts with a stretch inside Natural Bridge Caverns, part of the Comal Caverns network, before emerging onto the surface through beautiful trails over flowing hills and wooded landscape near San Antonio. Late September in this part of Texas can still run warm during the day, especially punishing for Last Person Standing racers logging loop after loop through the afternoon heat before things cool off overnight.

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This guide is independent and for planning only. The course details, dates, cutoffs, and format 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.