Sonoma Mountain is a subset AVA of Sonoma Valley. Sonoma Mountain is a freestanding mountain range that starts gently enough almost from San Pablo Bay and extends, arching sharply upward midway up the valley at around Glen Ellen, and then gradually descends into oblivion right at Santa Rosa. It is a geographical bell curve set on end in what would otherwise be a very wide valley. It is the Sonoma Mountains that make Sonoma Valley so narrow.
Not much wine is produced from the Sonoma Mountain AVA. Laurel Glen and Benziger of Glen Ellen wineries are the torchbearers.
Quoted from “Making Sense of California Wines,” Matt Kramer, 1992.