During the early years of winemaking in the Napa Valley, vineyards were often planted with many varieties growing side by side, as the practice of matching the grape varieties to the particular soil and climatic conditions of a site was not understood. 

Today, there is an intimate understanding of the connection between terroir and vine. Accordingly, winemakers have realized just how the diversity of Napa Valley’s soil, climate and terrain facilitates the growth of distinctive wines from specific sub-areas within Napa Valley.

This great diversity has led to federally designated defined grape growing areas within Napa Valley, giving them names that reflect their regional designations (known as American Viticultural Areas or AVAs).

Napa Valley is itself an AVA, and it has been since it received its own designation in 1981. It is California's first recognized AVA and the second in the United States. Within the Napa Valley AVA exist 17 nested AVAs.[i]

A vast array of soils of volcanic and marine origin coexists in Napa Valley, created by geological events that have occurred over the last 150-million years. The valley was formed by tectonic plate movement and volcanic activity, and the erosion and subsequent intermingling of this parent material has formed complex and highly varied soil compositions in the alluvial fans that emerge from the hillsides and spread out onto the valley floor. The most famous of these alluvial fans is the Rutherford Bench.

Further stirring up the geologic pot were the periodic encroachment of San Pablo Bay, which once reached as far as the site of present-day Yountville, and the flooding and movement of the Napa River along the valley floor.

This set of unique occurrences has given rise to soil diversity within the Valley that represents (a) half the world’s soil orders, (b) 33 soil series, and (c) more than 100 soil variations.

The structure and composition of the soil affect the character of the grapes and now guides the Napa Valley grape grower as to which rootstocks and grape varieties to plant. Each site presents its challenges and advantages to the winegrower.[ii]

Napa Valley vineyards are farmed to produce low yields which result in vivid, concentrated flavors in the grapes. Throughout the growing season, the canopy is carefully managed, usually by hand, to ensure optimal fruit development. Vineyard workers will tend to each vine, on average, more than twenty times during the year (a far different farming ethic than a few decades ago.)[iii]

For a winemaker, blending grapes from different vineyards means being able to make a wine of greater complexity. Alternatively, a winemaker can craft a unique, distinctive wine by focusing on a single vineyard. Winemakers in Napa Valley are famous for creating both beautifully blended wines from multiple sources, and distinctive wines from a single vineyard, i.e., To Kalon Oakville.

Napa Valley winemakers use a combination of the latest research and equipment, intuition, and practical experience to make distinctive wines. Given the wide range of wines produced here, winemaking methods have evolved, and vintners have gained an intimate knowledge with the art of winemaking that brings out the best from a specific vineyard[iv].

[i] Including: Atlas Peak, Calistoga, Chiles Valley, Coombsville, Crystal Springs of Napa Valley, Diamond Mountain District, Howell Mountain, Los Carneros, Mt. Veeder, Oak Knoll District of Napa Valley, Oakville, Rutherford, St. Helena, Spring Mountain District, Stags Leap District, Yountville, and Wild Horse Valley

 [ii] Valley floor soils tend to be deeper and more fertile and produce vigorous growth so the crop must be managed to produce concentrated grapes. On the hillsides, vines must struggle to survive in the spare, rocky soils and naturally set a smaller crop, producing smaller grapes of highly concentrated color and flavors.

 [iii] To further advance viticultural technology, Napa Valley is one of the only premium wine regions to have a university experimental vineyard. The UC Davis Field Station in Oakville.

 [iv] See Boone, V., Mastering Napa’s Mountain Appellations, Wine Enthusiast (https://www.wineenthusiast>Culture>Wine) for an excellent discussion of the history of the specific appellations.