Lake Sonoma 100K, 50K, TS Half Marathon – Geyserville, CA 2026

Join us in Healdsburg, California, on April 11th 2026 for the TERREX Lake Sonoma 100K, 50K, and Trail Sisters Half Marathon! We are excited to have adidas TERREX back as our presenting partner! We are stoked to team up with Mountain Outpost to bring you full livestream coverage, athlete panels, interviews, and commentary from special guests! Lake Sonoma 100K The 100K course will start with a climb up Pritchett Peak with a water only stop at the top. Once you reach the summit you’ll head back down toward the Lake Sonoma Visitors Center and then up to the hill to South Lake Trailhead where you’ll embark on an out and back of the original old school LS course and then back down the hill to the finish. It’s the same great Lake Sonoma Relentless experience, only this time with a big climb to kick it all off! Lake Sonoma 50K It’s not worth it unless you have to work for it! The 50k start is located in the green space next to the Lake Sonoma Visitor Center (you can’t miss it). After a short r