The Sierra de Guadarrama is the result of a clash between tectonic plates belonging to the South sub-plateau and the North sub-plateau, both part of the Iberian Peninsula's larger "Meseta Central" (Central Plateau). The mountain range was formed during the Cenozoic era (starting 66 million years ago), although the predominant material of which the mountains are composed (granite shelf tableland) was preexisting, having been laid down during the Variscan orogeny during the Paleozoic era when the continental collision between Laurasia and Gondwana occurred to form Pangaea. The mountains have undergone significant erosion since their formation, which is the reason why many peaks, especially in the northern and southern sections, have flattened summits, called "cuerdas" by mountaineers. For these reasons, the material making up the Sierra de Guadarrama is of more ancient origin than many other well-known mountain systems, such as the Pyrenees, the Alps, the Andes and the Himalayas.