Sean O'Brien 100K

The Sean O'Brien event, scheduled for January 31, 2026, in Calabasas, California, offers multiple race distances, including 100K, 50 miles, 50K, marathon (26.2 miles), and 30K. The race features scenic trail views and is suitable for ultrarunners and trail enthusiasts. The 100K race is a qualifier for the Western States 100.

Participants can register online, with registration opening in June 2025. The event provides a challenging and scenic trail experience, attracting runners from various levels who seek to test their endurance across different distances. Visit the organization's website for the most recent information.