Climate: Warm, due to greater protection from western hills, with less fog or wind incursions. The narrowing of the valley floor provides more heat reflection off the hillsides. Mid-summer temperature peak is often in the mid- to high 90°F range (31 to 35°C).
Elevation: 150 to 600 ft. (46 to 185m).
Rainfall: 38 to 40 inches (95 to 100cm) annually.
Soils: South and west borders are more sedimentary, gravel-clay soils, with lower fertility and moderate water retention. Further north and to the east soils are prevalently volcanic in origin and are deeper and more fertile.
Principal varieties and characteristics: Cabernet Franc, Cabernet Sauvignon, Merlot: deep, ripe, often jammy flavors, with firm tannins for structure, and appealing aromas of currant and black fruit. Rhone varieties (Syrah, Viognier): Fleshy, supple and slightly earthy. Zinfandel: Blackberry-like, well-structured.