The entirety of wine grown within Napa county falls within the Napa Valley AVA. Established in 1981, this is California’s most famous region, although it accounts for only four per cent of the state's vineyard plantings. There are now 16 sub-AVAs, scattered throughout the valley and the mountain slopes. The Valley itself is 50 kilometres long and eight kilometres wide and is surrounded on both sides by mountain ranges: Mayacamas to the west, separates Napa from Sonoma and provides protection from the coast; and Vaca to the east separates Napa from the desert-like Central Valley. The climate is moderate but heat spikes around harvest are common, and most rainfall occurs during winter – a starkly Mediterranean climate. Rainfall levels are similar to that of Bordeaux and the mountain ranges to the west provide rain protection to the valley on the east. The Napa Valley enjoys cool nights and a wide diurnal range. The warm conditions are moderated by the San Pablo Bay which brings in cool breezes and fogs in the morning – this effect dissipates as you move up the valley. Soils on the valley floor are alluvial and fertile while more rocky and volcanic types can be found on the mountains, and elevations can range from zero to 600 metres. It is easiest to categorise Napa Valley into mountain AVAs and valley floor AVAs as you dive into the complexity of what is a relatively compact wine region. Mount Veeder The Mount Veeder AVA, located west of Napa and Yountville, was established in 1990 and is home to just under 450 hectares of vines. Napa County does not allow plantings on slopes steeper than 30 degrees, rendering much of Mt Veeder unplantable and therefore one of Napa’s least developed AVAs. The region is on the southern end of the Mayacamas mountains with an easterly aspect, so moisture and cool air funnelled from San Pablo Bay find the vineyards easily. Shale, sandstone, clay and sandy loams are common soil types, along with a sub-surface layer of compressed ash rock which is very porous and creates a natural aquifer (which can facilitate dry farming). Most vineyards are located above the fog line and enjoy a strong diurnal shift. Oak Knoll District Located at the southern end of central Napa Valley, Oak Knoll was officially designated in 2004. It’s a region known for its long growing season, cooler conditions and very high-quality wines. It’s a relatively flat appellation and, together with Yountville, is considered among the Napa’s coolest areas. Soils are of deep loam and gravel and elevations range from 0-244 metres. The area is exposed to the oceanic influence from the San Pablo Bay, so fogs and cooling winds moderate the climate and provide long growing seasons with wide diurnal ranges. Daytime temperatures can reach 33 degrees Celsius, plunging to 10 degrees at night. Yountville The Yountville AVA, recognised in 1999, takes its name from George Yountville, the first person to plant vines in the area in 1836. Soil types vary from alluvial, silt, gravel and volcanic and elevations top out at 60 metres. The area is exposed to oceanic influences from the San Pablo Bay; fogs and cooling winds moderate the climate and provide long growing seasons with wide diurnal ranges just slightly smaller than in the Oak Knoll district. Oakville, Rutherford, St. Helena and Calistoga Continuing north from the Yountville AVA are Oakville, Rutherford and St. Helena, which sprawl across a number of alluvial fans in the foothills of the Mayacamas Mountains. Oakville is home to Napa’s most famous producers of the 100pt ilk: Harlan, Opus One, and Screaming Eagle to name a few. Rutherford, and then St. Helena, continue north in a similar vein until the valley floor comes to a point and ends in Calistoga – the warmest of the Napa Valley AVAs. Other Mountain AVAs Diamond Mountain District and Spring Mountain District are both north of Mount Veeder along the east-facing slopes of the Mayacamas Mountains on the west side of the Napa Valley. Howell Mountain and Atlas Peak are nestled in the Vaca at the north and south ends, respectively. A wide diurnal shift greatly influences the climate here. Valley Floor AVAs Several famed Napa AVAs are flanked by mountains on gently sloped foothills that reach into the valley floor. Some produce the most famous and sought-after wines from Napa Valley, and lie in close proximity (often within the same AVA) to the vigorous valley floor. Other Napa AVAs The Stags Leap District is a small western valley enclave surrounded by unplanted land that has a strong reputation thanks in large part to Stags Leap Cellars. The Vaca Mountains are far less planted than the Mayacamas Mountains. Chiles Valley lies east of the famed Howell Mountain, while Wild Horse Valley and Coombesville are at the southeast end of Napa Valley. Along with Chiles Valley, the latter two have not achieved the fame and reverence the rest of Napa enjoys. Lake County Eight AVAs make up an area that has long supported the Napa industry, providing quality Cabernet Sauvignon for inclusion in many blends.