The Lérins islands and islets, like the Tradelière, are formed of limestone rocks. They more specifically consist of well stratified and arranged in banks ash gray dolomites dating back to the Hettangien, the first stage of the Jurassic period. The limestone cover of the archipelago would have detached from the continental liasic mantle from the Pezou peaks north of the Cannes basin. It is believed to have been carried by the alpine uplift beyond the California hill. The limestone rocks would then have been retained by a resistant base in the bay of Cannes, giving birth to the five islands visible today.