Rain on the eastern slopes runs into the Rhone valley and hence out to the Mediterranean, whereas the rain on the western slopes of Mont Lozère gives birth to the River Tarn, which runs westwards towards the vast limestone plateau of the western Cévennes. This is sliced into 3 main areas ('causses') by the deep gorges of the rivers Tarn and Jonte. The causses are relatively flat and arid, and make perfect vulture country. The views as you approach the steep gorges are heart-stopping, as they plummet 500 metres (half the height of Ben Nevis) to a verdant river snaking below. The Tarn then has a long and tortuous journey across France to the Atlantic at Bordeaux.
The rest of the area is patterned with wooded mountain ranges of schist , with steep-sided river valleys hurrying their clear waters south-westerly to the Rhone valley. The most famous road across this is the Corniche des Cévennes. An ancient 'draille' (a track for the sheep on their transhumance) running parallel to this makes an unforgetable walk.