 From the end of the Paleozoic and during the Mesozoic (250 to 66 mya), the processes of erosion began to wear down the contours of the land.In this last period occurred a monumental departure from the ocean, which left subaquatic zones exposed on the surface (prior to this, it is likely that the sierra was not more than an islet raised slightly above the sea) and formed sinks of sediment that covered the plains with sediment and would give them their later calcareous character.In the Cenozoic (66 to 1.8 mya), the processes that raised the Peñalara massif and divided it into the blocks we find today began to work again.