Diablo Trails Challenge 2027

Diablo Trails Challenge starts and finishes at Castle Rock Recreation Area in Diablo Foothills Regional Park in Walnut Creek, with Mount Diablo as the main playground. Brazen Racing hosts the trail-running series, which offers a 5K, 10K, half marathon, and 50K, so the same event can suit a first trail race or a long day out for experienced ultra-runners. All races are professionally timed, finishers receive medals, and the event is part of the Ultra Half Series. The longer routes reach well beyond Castle Rock, linking parkland such as Round Valley, Los Vaqueros Watershed, Morgan Territory, Mount Diablo State Park, and Shell Ridge Open Space before returning to the start area. The half marathon is listed as a 13.5-miler and includes hill climbing, quick descents, and runnable rolling sections. The race also serves a local conservation purpose: it raises money for Save Mount Diablo, with part of every entry fee going to the group. Save Mount Diablo has spent more than 50 years preserving and expanding open space around the mountain, helping grow protected land from 6,788 acres to more than 120,000 acres.