Snell Valley is a depression landform in Napa County, California, about five miles north of Aetna Springs, known especially for its spring wildflowers and for the Missimer Wildflower Preserve within it, where the gold nugget lily grows. Historically, the valley was part of Rancho Guenoc, included in a Mexican land grant in 1845. Its name is generally associated with George and Hiram Snell, brothers from Germany recorded as residents of the Guenoc Rancho in 1857. In recent times, the valley was affected by the 2020 Hennessey Fire, a major wildfire that burned more than 315,000 acres across five counties and caused evacuations there.