The Rocher de La Baume and the cluse (close valley) of Sisteron form a topographical and climatic gateway opening onto Provence and offering a large bare rock sculpted like a cathedral in the words of the poet Paul Arène. This Tithonian bar consists of vertical limestone strata whose disordered folds and creases are famous worldwide and have become a curiosity for geologists. The layers of calcareous sediments deposited at the bottom of the sea at the end of the Jurassic were first folded at the end of the Mesozoic Era during the formation of Mont Ventoux and the Montagne de Lure and again later during the uplift of the Alps in the Tertiary.