 During the late Pleistocene , Calabozos erupted tuff composed primarily of rhyodacite and dacite . Three distinct eruptions have taken place within the last million years . The sheets of remaining ash left over from all of the eruptions together range from 200 cubic kilometres ( 48 cu mi ) to 500 cubic kilometres ( 120 cu mi ) in volume and are known as the Loma Seca Tuff . 
