Colorado River Run: 100-Mile & 50-Mile Ultra, 50K, Marathon, Half-Marathon, 10K and 5K

JUNE 27, 2026.

This will be the second event in the 2026 Capt'n Karl's Night Trail Run Series - held at Muleshoe Bend LCRA Recreation Area, approximately 40 miles northwest of Austin in picturesque Spicewood, TX. Muleshoe Bend is located on the scenic Lower Colorado River, Lake Travis region. This course is challenging, rocky, technical with 3094 feet of elevation gain. These trails are deceptively tough, with heat & humidity making Muleshoe Bend a worthy adversary. This is primarily due to the thick foliage & heavy woods, creating a peaceful environment & no wind. Get ready to sweat.

While every racer will get some cool swag, June 4th is the deadline to get a shirt.

Austin Solstice Circuit Challenge

The Fastest Summer Ultramarathon in Texas

July 25 & 26, 2026 | Pace Bend Park, Lake Travis

Set a PR!

Scenic Hill Country Course

Experience the breathtaking beauty of the Texas Hill Country as you run on smooth paved roads winding through majestic oak trees. With Lake Travis as your backdrop, this picturesque route combines natural beauty with the perfect running surface for speed and comfort.

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Set your sights on a personal record at the Austin Solstice Circuit Challenge. This unique event features a perfectly engineered 1.64-mile paved loop with an elevation gain of just 33ft at scenic Pace Bend Park on Lake Travis, designed for speed and performance even in July.

Race Distances

52.7 Mile Race

Loops: 32

Distance: 52.7 mi

Start: 7:00 PM 07/25

50K

Loops: 19

Distance: 31.0 mi

Start: 7:00 PM 07/25

Marathon (USATF Certification code: TX25015LAB)

Loops: 16

Distance: 26.35 mi

Start: 7:00 PM 07/25

25K

Loops: 10

Distance: 15.5 mi

Start: 7:00 PM 07/25; 7:00AM 07/26

10K

Loops: 4

Distance: 6.2 mi

Start: 7:00 PM 07/25;

7:00 AM 07/26

5K

Loops: 2

Distance: 3.1 mi

Start: 7:00 PM 07/25

7:00 AM 07/26

Carpe Diem 60

One Hour. One Sunrise.

Beat the heat.

Seize the morning.

Earn your day.

Start: 6:00 AM 07/26

7:00 AM 07/26

Why Choose This Race?

Fast, PR-Friendly USATF Certified Marathon Course (Boston Qualifier)

Unlike typical Texas summer ultras with brutal heat and technical trails, our smooth asphalt loop with minimal elevation gain creates ideal conditions for record-setting performances. This is a USATF-certified course: Certification code: TX25015LAB.

Evening Start Format

Race as the sun sets and July's magnificent Buck Moon rises over the limestone bluffs. Our strategic evening start times for longer distances mean cooler temperatures when you need it most.

Pacers Allowed

While we won't be providing official pacing groups for the Austin Solstice Circuit Challenge due to our size, we enthusiastically welcome personal pacers for both the Marathon, 50K and 52.7 Mile Solo events. Personal pacers can join Marathon and 50K participants after 8 loops and 52.7 Mile runners after 16 loops (approximately halfway points). Each pacer must pay a $15 fee that covers park entry, administrative costs, and an official pacer bib. Pacers need to sign a waiver and wear their designated "PACER" bib while on course. Runners are responsible for arranging their own pacers, but the loop format makes it particularly convenient for your support crew to join when you need them most. We find this flexibility is especially appreciated by first-time marathoners and ultra runners who benefit from personalized support during the challenging later miles as day turns to evening.

Pickup Information:

Saturday Packet Pickup:

Available from 4:30 PM to 6:30 PM.

Race Day Pickup:

For those unable to attend on Saturday or who prefer to pick up on race day, same-day packet pickup will be available Sunday morning from 5:30 AM to 6:30 AM.

Carpe Diem 60

One Hour. One Sunrise. Start your day with purpose.

Carpe Diem 60 is a 60-minute sunrise endurance challenge on this out-and-back course. At 6:00 AM, you’ll have one hour to cover as much distance as possible with early morning focus. Most Distance Covered Wins

Beat the heat. Seize the morning. Earn your day.

Course Details

The distinctive figure-8 course winds through the breathtaking Hill Country landscape of Pace Bend Park, featuring limestone bluffs, majestic oak trees, and views of Lake Travis. The smooth asphalt surface throughout makes it perfect for both day and night running, with the main loop connecting to a smaller upper loop.

• Surface: 100% smooth, paved asphalt – ideal for consistent pacing

• Elevation: Minimal gain per loop – gentle, predictable terrain

• Loop Length: 1.64 miles in a figure-8 configuration

• Scenery: Limestone bluffs, oak-covered hills, and Lake Travis views

• Aid Station: Access every 1.64 miles at the start/finish hub

• Marking: Fully marked with reflective markers for nighttime visibility

"Whether you're chasing a PR, a qualifying time, or simply want to experience the joy of running fast through a Texas summer night beneath towering oaks and limestone cliffs, the Solstice Circuit Challenge offers a rare opportunity to push your limits under optimal conditions."

Amenities

Aid Station

Fully stocked station at the start/finish hub

Restrooms

Convenient toilet vault facilities

Camping

First-come, first-served sites surrounding the course

Parking

Multiple areas for easy access

Finisher Awards

Medals and custom challenge coins for all finishers

Commemorate your achievement with a premium custom-designed medal featuring Lake Travis. These coins are part of the Race Austin Series: Collector's Challenge, which allows you to exchange three same-tier coins from different Fit Foundation races for a complimentary race entry of the same tier.

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Join Us for an Unforgettable Experience

Race from sunset to stars beneath the Buck Moon on the fastest summer ultra course in the Texas Hill Country.

REGISTER NOW!

Ready to prepare? Check out our comprehensive training guide designed specifically for the Solstice Circuit Challenge.

August 8th, 2025.

This is the culminating event in the Capt'n Karl's Trail Series at one of the best privately owned adventure parks in all of Texas, the amazing Reveille Peak Ranch! This park is located 55 miles northwest of Austin in the historic town of Burnet. The amenities at RPR are first class & we will be taking advantage of this by providing our runners, spectators & volunteers with a series finale party. But first, runners will be treated to unique & spectacular geological formations. Navigating over large rock domes with amazing views, while tackling the most elevation gain of our four venues (3812 ft). This course really has it all….single track, exposure, tree-covered woods, hills & technicality. All to challenge even the most seasoned trail runner.

While every racer will get some cool swag, July 16th is the deadline to get a shirt.