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Sean O'Brien 100K

Calabasas, United States • 31 Jan 2026

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.

United States California Calabasas

Race information

Website Registration
100 km
100k
50 mi
50 Miler
50 km
50k
26 mi
26.2
30 km
30k
Visit the organization's website for the most recent information.
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