Mueller Family Vineyards is located on ten acres on Diamond Mountain near Calistoga. The Diamond Mountain District or AVA is located above the valley floor, west of Highway 29 between Calistoga and Spring Mountain, north of St. Helena. Most of Diamond Mountain and its peak are actually in Sonoma County, but the winegrowing reputation of the mountain has always been associated with the Napa Valley side. It encompasses some 5,000 acres, of which less than 500 are planted to vines, making this the smallest AVA in the Napa Valley. The name, “Diamond Mountain” apparently comes from the plentiful obsidian found here.