Carneros soils are among the youngest in Northern California. The clay loam and marine sediments were deposited and exposed some 10,000 years ago when the inland sea known as Lake Corcoran breeched its natural dam. It carved the Carquinez Strait and filled both the San Francisco and San Pablo Bays en route to where the Golden Gate now spans the entrance to the Pacific. Under the youthful clay soils are deposits of fractured sandstone and denser clays.