The soils of the Southwest lie mainly on the Tertiary sedimentary lands of the Aquitaine Basin and on the ancient alluvial deposits of the Quaternary period terraces. The vineyard is planted on clay-limestone soils, sands, pebbles, clays, grey limestones with a clay subsoil. The geological activities contributed to split this region into many sub-regions showing diversity in their soil composition. Soils and subsoils are often poor with good drainage, which is favourable to the cultivation of grapes.