Tarn (river) a mean flow of approximately . The Millau Viaduct spans the valley of the Tarn near Millau, and is now one of the area's most popular attractions. The tributaries of the Tarn include: The Tarn separates the Narbonne and Aquitaine basins. The Tarn passes through the following departments and towns: The Millau Viaduct, the tallest bridge in the world, carrying the A75 autoroute across the Tarn Gorge near Millau, opened in December 2004. The Tarn is famous for its brutal floodings, which are the most dangerous in Europe along with the Danube. The flooding of March 1930 saw the Tarn
Bleu des Causses refining fourmes is much more restrictive. It concerns some regions of the district of Millau: Campagnac, Cornus, Millau-Ouest, Millau-Est, Peyreleau, Saint-Affrique, and at the towns of Trèves and of Pégairolles-de-l'Escalette. The terroir includes, among others, land caussenardes who gave their name to this cheese. These are characterized by a limestone subsoil drainage, causing drought when rain are scarce. Rich soil is low, giving short and bushy vegetation. However, this naturally sparse vegetation is aromatic and contributes to the flavor of the milk. The refining zone has vertical limestone cliffs carved by the erosion of the rivers Tarn, Doubie, and Jonte.