The Rocher de La Baume at Sisteron (Alpes-de-Haute-Provence). This remarkable structure does not correspond to a sharp anticlinal hinge, as one might think, but to the meeting of two benches, due to their bevelling by an overlapping surface. The town of Sisteron owes its strategic position to the fact that it rests on a vertical tithonic bar, which the Durance crosses via a narrow "clue" (a Provencal term equivalent to cluse*). This rocky bar forms a border between the Laragne depression to the north and the Lure mountain and Valensole basin to the south. France