Guenoc Valley is a small inland valley comprising an alluvial fan of Arroyo Seco and Conejo Loam series soils isolated from surrounding areas by rocky ridges. Its geographical location also affects the climate. Guenoc Valley has slightly less rainfall than the nearby Middletown area. Guenoc Valley receives approximately to of rain per year, while Middletown receives approximately per year. Guenoc Valley also experiences slightly greater seasonal temperature extremes, being warmer in the summer and colder in the winter. Also, due to the surrounding ridges, fog is generally less severe than in Middletown. For these reasons, the United States Department of the Treasury Alcohol and Tobacco Tax and Trade Bureau determined that Guenoc Valley possesses geographical features which distinguish the area viticulturally.