Sean O'Brien 100K
JAN
31
2026
Run the scenic Sean O'Brien Trail Races in Calabasas on January 31, 2026, with distances for every trail runner. The 100K is a Western States 100 qualifier, and options from 30K to 50 Miler promise challenge and community.
Sat 31 Jan 2026
100 kilometers
50 miles
50 kilometers
26 miles
30 kilometers
Always double-check with the organizer's website! This page may contain affiliate links.
Event overview
The Sean O'Brien trail races take place on Saturday, January 31, 2026, in Calabasas, CA. The event is based at 1925 Las Virgenes Road. Multiple trail race distances are offered on the same day. The 100K distance is a 2026 Western States 100 (WS100) qualifier.
Race details
Distances offered:
- 100K
- 50 Miler
- 50K
- Marathon (26.2)
- 30K
Registration closes Friday, January 2 at 11:59 PM PT. The event listing includes course view references such as Mile 7 and Mile 15 views. 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
