Shannon Ridge Vineyard in foreground with Clear Lake and Mountain in Background California is filled with beautiful and unique wine-growing regions, but none quite as exciting as the High Valley AVA. It sits at over 1,600 to 3,000 feet above sea level with a ring of mountains surrounding a volcanic valley. Back in the 1870s, High Valley created a name for itself as one of California’s largest wine producing regions before Prohibition. When viticulture came to a standstill during Prohibition, the valley was reworked for crops such as walnuts and prunes. Now, High Valley is home to some of the most intriguing winemaking in California. But what exactly makes it one of the most unique growing regions?