The Rocher Rond is mainly composed of limestone. The western slope is almost exclusively exposed rock and cliffs, overlooking the Lac du Lauzon, and the summit massif is of the Santonian strata, whilst some of the surrounding mountains are of another Cretaceous strata, the Barremian. However, this lies on top of another rock strata, of the Neocomian era, which is exposed below the cliffs in a concave slope descending to the shore of the Lac du Lauzon.