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Chamoson belongs to a geological formation characterized by large outcrops of limestone, shale and slate covering the European continental basement, itself composed of granite and gneiss. The vineyards of Chamoson sit on three distinct geological formations with widely different soils and forms. Ninety percent of Chamoson’s vineyards are planted within a large dejection cone containing alluvial deposits. The cone, which was formed for the most part 5,000 years ago, is composed of aalenian shale (Middle Jurassic or Dogger) and metalimestone carried down from Haut-de-Cry and Ardèvaz by the Losentse, Cry and Saint-André torrents. The cone contains no trace of Rhodanian moraine. It has a relatively gentle downward slope and is quite permeable to water. The rest of the vineyards are planted in terraces on glacial and moraine deposits dating from the last glacial period of the Quaternary. These are the remains of local glaciers that developed on the eroded remains of the massive Rhodanian glacier as it retreated from what is now the Rhône Valley. The soil here is characterized by an abundance of limestone material of diverse structure, silt, and coarse sand, as well as gravel and pebbles mixed with clay in places. A water supply study conducted at the Chamoson vineyards confirmed the decisive role moderate water stress plays in the ripening of grapes. The study focused on two terroirs typical of the Chamoson vineyards: a) plots rich in fine alluvials and organic matter, ideal for growing red wine varieties. Located mainly along the edge of the Losentse, these plots are particularly well served by the loamy waters of the Torrent du Cry and the Tséné; b) dry, stony limestone plots containing black slate, particularly well-suited to growing Johannisberg, the emblematic wine of Chamoson. These parcels are found along crests and hillsides with good exposure to the sun’s warmth. To varying degrees, alluvia from the Losentse River have contributed a limestone component to the region’s soil, making it relatively acid. Variations in this effect explain the wide range of grape varieties that are grown here. The vineyards are organized into nineteen grape variety sectors, corresponding to nineteen terroirs that still bear ancient names that were attributed by ancestors and remain a precious heritage of their observational skills and practical knowledge:
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