4. Soil is a crazy quilt in California; loam, clay, limestone, you name it. The earthquake-prone state has seen its share of tectonic activity, so though surface dirt might be one mix (iron-rich, for instance, as in this photo taken at Chappellet Winery in the Napa Valley), a meter down, the vine roots might reach into different soil. Also, soil content and quality vary across vineyards. With the advent of winemaking focused on using grapes from only a few vine rows, these nuances show up in the wine. As Boulton says, "Terroir is a changing variable. That's what's exhilarating."