Sean O'Brien 100K
JAN
31
2026
Challenging trail races in Calabasas on Jan 31, 2026 offer distances from 30K to a WS100 qualifying 100K, plus 50 Miler, 50K and marathon. The event is sold out now but a waitlist is available for hopeful runners.
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, California. The event base is listed at 1925 Las Virgenes Road, Calabasas, CA. The 100k distance is designated as a 2026 Western States 100 (WS100) qualifier. The organizer’s page notes the event is currently sold out and that a waitlist is available.
Distances and registration
- 100K
- 50 Miler
- 50K
- Marathon (26.2)
- 30K
Registration for the event closes on Saturday, November 15 at 11:59 PM PT. The event listing references course views at Mile 7 and Mile 15. 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
