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Sean O'Brien 100K

Calabasas, United States • 31 Jan 2026

The Sean O'Brien event in Calabasas, California, offers multiple trail running distances including 100K, 50 miles, 50K, marathon, and 30K. The 100K race serves as a qualifier for the 2026 Western States 100. The course features scenic trail views with notable vantage points around miles 7 and 15, providing runners with beautiful natural surroundings. This event is well-regarded for its challenging terrain and supportive atmosphere, attracting ultrarunners aiming for qualification and personal achievement. Registration closes mid-November, and the race takes place in late January, making it a key early-season trail running event. 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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