Mostly sound limestone which is unstable on certain routes (easy, not too steep ones). Descent is by abseil down a scree-gully and requires GREAT care. Big peak you see on the road to Barcelonnette from Lac de Serre-Ponçon.
Drive up to pretty much the end of the road of the Laverq Valley (off main road between Le Lauzet and Meolans at La Fresquière). Access is obvious.