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 in the volcano group took place SSE of Monte Tronador, where the Fonck cinder cone (also known as Cerro Volcanico) overlies rocks of the Steffen volcano group SE of Tronador. 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.