Located in the northwestern portion of Yolo County, the Dunnigan Hills AVA encompasses 69,000 acres with roughly 1,300 acres hosting vines. The summer days are hot, averaging between 95°F and 98°F, but at night the temperatures cool to between 55°F and 65°F. This tremendous drop in temperature allows the grapes to cool, which preserves the grapes' natural acidity. The soil composition is a gravelly loam in the upper hills, whereas in the valleys it is silty or chalky clay loam over sandstone. Dunnigan Hills is home to only one winery, R. H. Phillips.