Embark on a challenging and rewarding trail adventure at the Annadel Half Marathon, 10K, and 5K on April 18, 2026, in Santa Rosa, California. This beloved Sonoma County tradition is more than just a race; it's a non-profit fundraising event dedicated to preserving and enhancing Trione-Annadel State Park, where a portion of the proceeds supports park maintenance and improvements. Runners can expect typical race day conditions with highs around 70F and lows around 44F, and a low 8% chance of precipitation, making for pleasant running weather.

The Half Marathon course is renowned as a hilly and technical trail designed for experienced runners, featuring over 1,500 feet of elevation gain across rocky and rooted terrain. Participants will traverse 100% unpaved trails, immersing themselves in gorgeous scenery of green meadows, wildflowers, and a variety of beautiful trees as the route winds through Spring Lake Park before climbing into Annadel State Park. The 10K also offers a tough course with significant elevation gain, while the 5K presents a hilly, out-and-back gravel fire road, providing a scenic introduction to trail running for all levels.

Starting near the Spring Lake Oak Knolls picnic area, the event promises excellent race-day support with chip timing, a commemorative event shirt, a finisher medal, and post-race beverages and snacks. In line with its park stewardship mission, the Annadel Half Marathon is a low-waste, cup-free event, encouraging runners to bring their own water bottles for refills at aid stations. With a 4-hour cut-off time for the half marathon, this race offers an exhilarating experience, celebrated by a supportive community and breathtaking natural beauty.