The shallow depth of the sea that covered the Luberon region over 100 million years ago as well as its chemistry and temperature have led to the appearance of a green clay known as glauconite, rich in reduced iron. Emerged following tectonic thrusts, the glauconite-rich sand was exposed to the percolation of heavy rains from the humid tropical climate of the Cenomanian age that induced many chemical reactions that led to the formation of the ocher quarries in the area.