The Calistoga AVA is an American Viticultural Area located in the northern portion of California's Napa Valley AVA. The appellation is distinguished by its volcanic soil, high temperatures up to 100 °F (38 °C) during the day, and cool nights during the growing season due to breezes from the Russian River, causing the highest diurnal temperature variation in the Napa Valley—up to 50 °F (28 °C).