Missimer Wildflower Preserve is a protected grassland in Snell Valley of Napa County, California, valued for its diverse native flora. Owned by the Land Trust of Napa County, it occupies significant serpentine soils, a difficult ground type that supports specially adapted plants and gives the landscape much of its distinct character. In the Snell Creek watershed, this unusual habitat is especially known for its wildflowers, including the yellow mariposa lily, Calochortus luteus.