The Carneros District lies at the south end of both the Napa and Sonoma Valleys. An area of low hills and flatlands, the region is profoundly affected by cool marine air from the bay and Pacific Ocean. During the summer, a ceiling of fog hovers over the Carneros vineyards in the morning, burning off as the day goes on. Specifically on the Schug Estate, the fog is replaced at midday by summertime winds that come rushing through what is known as the Petaluma Gap, a break between two mountains which creates a kind of wind-tunnel across the vineyards. The wind stress causes the skin of the grapes to thicken, particularly the higher Pinot Noir plantings, a characteristic that adds pepper and spice nuances to the wine.