The Tronador volcanic group straddles the Chile-Argentina border east of scenic Lake Todos los Santos. Activity dates back to the early Pleistocene, and the most prominent part of the dominantly basaltic-to-andesitic complex is the prominent, glacier-covered Monte Tronador volcano, which formed in three stages during the mid-Pleistocene. The only possible Holocene activity took place SSE of Monte Tronador, where the Fonck cinder cone (also known as Cerro Volcanico) overlies rocks of the Steffen volcano group. The well-preserved cone was the source of a single andesitic lava flow that postdates the last glacial cycle dating back to 70,000-14,000 years ago and has variously been inferred to be of latest Pleistocene or Holocene age.