Diablo Summit Stomp 2026

The Diablo Summit Stomp is a trail race held in Walnut Creek, California, on the slopes of Mount Diablo, east of the San Francisco Bay. It takes place in October and features four distances: 30K, half marathon, 10K, and 5K. All courses are on trails; weather can bring mud and creek crossings, making it a rugged trail event rather than a smooth road race. Walkers and hikers are welcome in all distances, catering to both novice trail runners and experienced hill runners. All distances begin near the Castle Rock Park area off Castle Rock Road. Mount Diablo reaches just under 4,000 feet. The park's established trails, used for hiking, walking, horseback riding, and camping, feature rocky terrain that contributes to the race's distinct Diablo character. The event supports Save Mount Diablo, with funds raised for protecting the mountain and adjacent parkland. Age-group awards are given three deep in five-year categories, and volunteer photographers provide free race photos.