Another Napa Fun Fact: There are a variety of growing appellations (see picture) in the valley that produce different types of grapes. Much has to do with the soil. On the west side of the valley the mountains were formed by a earthquake. They receive the wind of the Pacific. This results in much growth and organic matter. On the east side of the valley the mountains were formed by volcanic activity. They are rocky and high in mineral content. Also, the further north you go the warmer the valley and the further south you go—toward the Bay—the cooler. This determines which grapes can thrive where. All this results in many high quality wines, yet different wines and grape combinations, giving us some of the best wine in the world.