Altitude and its impact on microclimate is integral to the success of Chiles Valley’s winemakers. High above the fog line and far from the coast, vineyards in this AVA are denied the cooling effects of the marine air and fog that temper the heat on the valley floor. Instead, they rely on their altitude and the accompanying diurnal temperature variation to ensure that grapes are able to cool overnight and thus balance their ripe fruit flavours with all important acidity. Vineyards are planted here at elevations of between two-hundred and four-hundred metres above sea level exposing them to strong winds which again serve to lower temperatures. On the steep hillsides, stony clay soils with good drainage dominate, whilst closer to the valley floor more fertile silty soils encourage undesirable high yields. In addition to the aforementioned [Zinfandel](/zinfandel) and [Cabernet Sauvignon](/cabernet-sauvignon) varieties, a number of other red grapes are grown in the appellation, but in much smaller quantities; these include but are not limited to [Cabernet Franc](/cabernet-franc), [Merlot](/merlot) and [Petite Sirah](/petite-sirah). Of the white grapes cultivated in Chiles Valley, [Chardonnay](/chardonnay) is predictably the principal variety with some support from [Sauvignon Blanc](/sauvignon-blanc) and [Sémillon](/semillon). With a viticultural heritage stretching back to the 1870s, Chiles Valley is today, by [Napa](/ava/napa-valley-ava) standards, a relatively small and somewhat obscure appellation. Just four-hundred hectares of its total area is planted to vine and the wineries that operate from here are mostly of the family-run, bespoke kind. Nevertheless, it is beginning to earn recognition for its big, structured reds with a distinctive cherry / blackberry flavour profile.