In the Neogene the low angle subduction of the Cocos Plate led to volcanism in the now extinct Cordillera de Aguacate chain in the center of the country. The Valle Central basin formed as volcanism shifted northeastward in the Quaternary. In the Pleistocene, calderas ejected huge quantities of silica-rich ash, filling the Valle Central basin, affecting the Tarcoles Gorge and generating the Orotina debris fan at the coast.