Sean O'Brien 100K/50M/50K/26.2/30K

Embark on an unforgettable trail running adventure at the Sean O'Brien 100K/50M/50K/26.2/30K, set in the breathtaking Santa Monica Mountains of Calabasas, California, on January 31, 2026. This challenging event, first run in 2014, was meticulously mapped by Sean O'Brien and race director Keira Henninger to deliver one of the West Coast's most epic courses, born from a desire to offer a tough winter race in a truly spectacular setting after the original Ray Miller course was impacted by fire.

Runners will traverse a demanding course that is 95% un-paved, featuring a mix of beautiful single-track, fire roads, and technical sections along the iconic Backbone Trail. Prepare for significant elevation gains—up to 16,096 feet for the 100K, around 10,000 feet for the 50M, and approximately 6,400 feet for the 50K—all while being treated to sweeping ocean vistas and rarely touched backcountry trails. Typical race day conditions in late January offer pleasant temperatures, with highs around 71F and lows near 43F, alongside a low 10% chance of precipitation, though creek crossings are a common and refreshing feature of the course.

Starting and finishing at Malibu Creek State Park, the Sean O'Brien races are renowned for their challenging nature, including stringent cut-off times. Aid stations are well-stocked with sweet and salty snacks, PB&Js, potatoes, fresh fruit, and electrolytes, but runners must be self-sufficient and carry their own hydration vessels as it is a cupless race. The 100K distance proudly serves as a qualifier for the prestigious Western States 100, while the 50M is a Sterling Silver Ticket Race for the Angeles Crest 100, drawing a competitive field. Whether you're aiming for a qualifier or seeking an unforgettable journey through California's stunning mountains, the Sean O'Brien Trail Runs promise a truly memorable and rewarding experience.