The Roques de Garc燰 are erosional remnants of the Ca鎙das series rocks. The Ca鎙das series of volcanic materials follow the Miocene basalts with an erosional unconformity and consist of a lower and upper Ca鎙das series of darker and lighter extrusive rocks and lavas, respectively. The type of erosion that has taken place here, tafoni (or cavernous) erosion, takes place where there are high temperature and humidity differences. It is a combination of physical and chemical weathering processes, and starts when water brings dissolved minerals to the rock surface. When the water dries, the minerals form crystals that force small particles to flake off the rock. Eventually, large cavities such as these form, having a cavernous and honeycombed shape because the surface layer of rock is harder than the interior.