Like the Maures and Tanneron massifs surrounding it, the Massif de l'Estérel is a relic of the Hercynian range. It is separated from the Maures by the Argens valley to the west and extends south as far as under the Mediterranean sea. Such continuity is evidenced by the red rocks - porphyric rocks mainly of rhyolite - of the coastal creeks and the color of the rocks that outcrop as islets here and there.