The Diamond Mountain District AVA is an American Viticultural Area located in California's Mayacamas Mountains in the northwest portion of the Napa Valley AVA. The appellation sits at a higher elevation than most of Napa Valley's wine region, resulting in less cool fog coming in from San Pablo Bay, and more direct exposure to sunlight. The soil of this AVA is volcanic and very porous which allows it to cool down quickly despite the increased sunlight.