In order to understand the geology of the Massif des Ocres in Luberon, one must imagine what the continent was like over 100 million years ago. At that time, an ocean opened up in place of the Alps, the Pyrenees did not yet exist, and a large sea arm crossed France from north-west to south-east. At the site of what is now the Provençal Colorado of Rustrel was a shallow sea at the bottom of which sands were deposited.