Sean O'Brien 100K

Calabasas, United States • 31 Jan 2026

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.

Race information

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.
Trail runs nearby

Run or hike to the iconic Hollywood Sign through scenic Griffith Park, with 8M, 8K, 5K and a kids 2.2K option. Enjoy skyline views, chip timing, finisher medal and post race refreshments in a true LA outdoor experience.

Run or hike through Griffith Park to the iconic Hollywood Sign on out and back courses ranging from a kids run to 8 miles. Enjoy skyline views, chip timing, aid stations and a finisher medal.

Run scenic backcountry trails at Boney Mountain Trail Run in Newbury Park on February 7, 2026, with half marathon and 7k options. Expect rugged single track, ocean views, creek crossings and lively post race festival with tacos and awards.

Scenic Boney Mountain trail run in Thousand Oaks offers challenging half marathon or 7k routes with creek crossings, single track climbs and ocean views. Enjoy race shirts, medals, free photos, vegan breakfast and a $500 course bonus.