Sean O'Brien 100K

The Sean O'Brien 100K is a premier trail running event taking place in Calabasas, California, featuring multiple race distances including 100K, 50 miles, 50K, a marathon (26.2 miles), and 30K. This event is recognized as a qualifier for the prestigious Western States 100. Participants can expect scenic views and challenging terrain as they navigate the trails.

Registration for the event opens on June 1, 2025. The Sean O'Brien 100K offers an exciting opportunity for runners of various skill levels to test their endurance and enjoy the beauty of the California landscape. Visit the organization's website for the most recent information.