Because Rioja's rivers originate in its limestone-rich mountains, even the soils on the valley floor contain considerable limestone, or calcium carbonate. On the hillsides, the soils can change dramatically with modest changes in elevation, shifting from chalky limestone to soils rich in clay or iron. These diverse soils produce subtle differences in the wines a boon to the winemaker at blending time. With these differences in altitude, climate and soil in mind, let's look again at Rioja's sub-regions. For more information about this series, please visit www.ciaprochef.com/rioja.