Calistoga AVA

Climate: Warm to hot, depending upon time of year; lower humidity; summer temperatures peak to 90°F (32.2°C) and fall to low 50s°F (11°C), the result of marine air from the northwest; cool afternoon and evening breezes .

Elevation: 300 to 1200 ft (92 to 370 m)

Rainfall: 38 to 60 inches (96.5 to 150 cm) annually

Soils: Almost completely of volcanic origin, soils range from rocky, stony loam on the hillsides, to gravelly or cobbly loams on the alluvial fans, to heavierclay-slit soils in the valley center areas

Principal varieties and characteristics: Cabernet Sauvignon: deep, ripe, often jammy flavors, with firm tannins for structure, and appealing aromas of currant and black fruit. Rhone varieties (Syrah, Petite Sirah ): Fleshy, supple and slightly earthy. Zinfandel: Blackberry-like, well-structured.

Oakville AVA:

Climate: Moderately warm, with temperatures commonly in the mid-90°F range in high summer, but also still strongly affected by night and early morning fog which helps keep acidity levels good. East side of the AVA receives more of warmer afternoon sun.

Elevation: 75 to 500 ft (23 to 150m) Rainfall: 35 inches (87.5 cm) annually

Soils: Primarily sedimentary gravelly alluvial loams on the western side, with more volcanic but heavier soils on the eastern side. Low to moderate fertility and fairly deep, with average water retention.

Principal varieties & characteristics: Cabernet Sauvignon, Merlot: Ripe currant and mint flavors, rich texture and full, firm structure tempered by rich fruit. Sauvignon Blanc: Full, steely, yet very fleshy, and not especially crisp.

St. Helena AVA

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.

Los Carneros AVA

Climate: Cool, with prevailing marine winds from the San Pablo Bay and through the Petaluma Gap to the west. High temperatures during summer rarely exceed 80°F (27°C) with less diurnal range variation. Ideal for sparkling wine grape production.

Elevation: 15 to 400 ft. (4.6 to124 m)

Rainfall: Lowest in Napa Valley: 18 to 24 inches (7.2 to 9.6 cm) annually

Soils: Clay dominated, very shallow in general, with more loam and hillside alluvials in the northern section. Yields typically are restrained by the hard claypan subsoil, which prevents deep-rooting.

Principal varieties & characteristics: Chardonnay: minerally pear-apple and spice flavors. Merlot: sinewy and lightly herbal, with fine tannins and sleek structure. Pinot Noir: ripe cherry-cinnamon spice flavors with earthy notes.