Lake Sonoma 100K

Event overview

The Lake Sonoma race weekend in Geyserville, California is on Saturday, April 11, 2026. The event includes three trail distances:

• 100K - Western States qualifying 100-kilometer ultra.
• 50K - 50-kilometer trail ultra with a bridge crossing.
• Trail Sisters Half Marathon - 13.1-mile, women-only out-and-back from Lone Rock to the Lake Sonoma Visitor Center.

The 100K route begins with a climb to Pritchett Peak, includes madrone groves and lake overlooks, and follows sections of the original out-and-back Lake Sonoma course. The 100K has 13 aid stations (8 full, 5 water-only); crew access is allowed at South Lake (outbound only), Warm Springs, and Liberty Glen. Finishers who complete the 100K in under 19 hours qualify for Western States 2027. The 50K features rolling singletrack, multiple aid stations, and a final downhill to the Visitor Center finish. The half marathon starts at Lone Rock, finishes at the Visitor Center, and has a shuttle from the finish back to the start.

Practical information

All races are cupless; each runner must carry a bottle, flask, or hydration bladder. Aid stations are stocked with hydration, chews, snacks, basic medical supplies, and sunscreen. Drop bags and crew access are available at designated locations on the ultra courses. Parking for the 100K and 50K is at the Lake Sonoma Visitor Center lots; half marathon parking is at Lone Rock. Vehicle and tent camping are permitted in the main lot Friday and Saturday nights. Approximate driving options include San Francisco International and Sacramento International airports. Registration opens October 1 with early and regular pricing tiers. Visit the organization's website for the most recent information.