Sean O'Brien 100K

JAN
31
2026
Read all about the Sean O'Brien 100K on 31 Jan 2026 in Calabasas.
Sat 31 Jan 2026
100 kilometers 50 miles 50 kilometers 26 miles 30 kilometers

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About the race

Sean O'Brien 100K/50M/50K/26.2/30K is a trail ultramarathon event in Calabasas, California (1925 Las Virgenes Road). It offers five distances: 100K, 50 miles, 50K, marathon, and 30K, giving athletes a range of challenging options on scenic trail terrain. The race is part of the Sean O’Brien Trail Runs series and uses local trail networks for the course.

A notable feature is that the 100K is a Western States 100 (WS100) qualifier for 2026, attracting ultrarunners aiming for a WS qualification. Registration closes November 15 for this event scheduled around January 31, 2026. Visit the organization's website for the most recent information.

100 km
100k
50 mi
50 Miler
50 km
50k
26 mi
26.2
30 km
30k

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