It took millions of years and the slow work of erosion to create the Clues de Haute-Provence. These steep, vertical canyons are the result of impetuous torrents cutting into the mountain ranges. The Clue d'Aiglun, named after the lovely hilltop village through which the D10 runs, was carved out by the Estéron. It's the most mysterious of them all: a few metres wide, 200m to 400m high, 2km long, it separates the Charamel Mountain and Mt St Martin.