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. Erosion of the rocky massif filled the basins with sediment. Glacial action in the Quaternary (1.8 mya to present) finished shaping the Peñalara cirque and the walls of the mountainous axis. The cirques were covered by a mantle of ice up to 300 m thick. Later, the confluence of the rivers gave the final touch to the landscape. The dominant rock in the park is granite, which is very hard and erosion-resistant.