The Next Loop Endurance Series - Lake Carl Blackwell
Lake McMurtry, United States • 21 Nov 2026
The Next Loop Endurance Series - Lake Carl Blackwell
The 40/50 Mile Challenge is a continuous loop trail race held at Lake Carl Blackwell in Stillwater, OK. Competitors run repeated laps on a clearly marked 3.1-mile (5K) loop and complete either 40 miles or 50 miles within a 12 hour time limit. The event runs alongside The Next Loop Endurance Series but is scored separately; Next Loop participants run on the hour while 40/50 Challenge runners race continuously.
The loop follows a scenic trail system with a mix of dirt paths, grass, and lightly packed earth. The route features gentle rolling elevation, wide sections, and generally good footing. Each lap returns to the same central start and finish area where a fully stocked aid station is available.
Logistics include designated personal staging areas where runners may access supplies each lap, permitted crew access in specified areas, and allowance for pacers under event rules. Medical and race staff are on site throughout the event. The centralized support and loop format keep navigation simple and allow runners to refuel, change gear, or receive crew assistance without leaving the course.
Location: Lake Carl Blackwell, 11000 W Hwy 51, Stillwater, OK 74074.
Distances offered: Visit the organization's website for the most recent information.
- 40 Mile
- 50 Mile