Three to five million years ago, Green Valley was a shallow inland sea, which slowly tilted and drained into the ocean. This left behind a series of fine sandy soil types which, with their balanced chemistry and slight variations in clay content, perfectly feed vine plants with nutrients and water.
The older geology of the appellation looks like a crazy quilt with patches of varying soils, a mixture of ocean floor rocks faulted together as the Pacific Ocean floor slid down and east under the edge of the continent 100 million years ago. Alluvium produced by rivers and streams eroding the older rocks and soils covers the valley floor.
The two major soil categories are the sandy Goldridge and the older rocky Franciscan. Classic Goldridge provides good drainage and exceptional, natural chemical balance. Franciscan soils are dominantly light brown, sandy clay loam with higher magnesium content, well suited to Green Valley’s cool climate.
The main soil-related factors in wine quality are water supply, history, soil chemistry and nutrient supply, all dictated by clay content and original parent material. The key—as with every aspect of winemaking—is balance.