Napa Valley is home to several alluvial fans, which consist of layers of gravel, sand and silt that have descended from the western Mayacamas Mountains over millennia.These soils are deep and well draining, which is a necessity if one’s goal is to produce intensely concentrated Cabernet Sauvignon wines. Such soils are so granular that gravity pulls water away from the vines, forcing them to chase after it. The result is smaller berries with more intense and flavorful wines.