The Tarn is a 380.2-kilometre long river in the administrative region of Occitania in southern France. It is a right tributary of the Garonne. The Tarn runs in a roughly westerly direction, from its source at an elevation of 1,550 m on Mont Lozère in the Cévennes mountains, through the deep gorges and canyons of the Gorges du Tarn that cuts through the Cau…The Tarn is a 380.2-kilometre long river in the administrative region of Occitania in southern France. It is a right tributary of the Garonne. The Tarn runs in a roughly westerly direction, from its source at an elevation of 1,550 m on Mont Lozère in the Cévennes mountains, through the deep gorges and canyons of the Gorges du Tarn that cuts through the Causse du Larzac, to Moissac in Tarn-et-Garonne, where it joins the Garonne, 4 km downstream from the centre of town.