The 2,400-foot Sonoma Mountain range begins to rise above the town of Glen Ellen at the western edge of the Valley of the Moon. Found here are high-altitude, steep-sloped vineyards, with eastern exposures to catch the fog-free morning sun. These vineyards fall within the larger Sonoma Valley AVA. However, due to the unique hillside terroir, they are entitled to use the more specific designation of the Sonoma Mountain AVA. The irregular folds and crevices of the mountain slopes also create microclimates suitable for limited production of a diverse range of other varieties.
The soil in the Sonoma Mountain AVA are mostly volcanic, made up of old lava flows and ash left over volcanic activity that shaped the region millions of years ago. These free-draining soils are largely devoid of any organic matter and suit the production of full-bodied reds.