Geology of Chile the Taitao Peninsula, the Peru–Chile Trench subduction zone is the boundary between the South American and Nazca Plates. At Taitao, the Chile Triple Junction and the Nazca Plate subduct the South American Plate. In Norte Grande the mountains form a series of plateaus, such as Puna de Atacama and the Altiplano. At a south latitude of 27 degrees, Chile's highest mountain (Ojos del Salado) reaches a height of . Below 42 degrees south, the Andes split into a fjord landscape and the highest mountain is Monte San Lorenzo at . As the mountains ebb, the snow line lowers; in the
Ojos del Salado of the Nazca Plate beneath the South America Plate became increasingly shallower and this caused volcanism to shift from the Maricunga Belt to the Ojos del Salado region. The Paleozoic basement crops out only northwest of Nevado Tres Cruces. Other geologic units in the region are Oligocene sedimentary units and volcanic rocks ranging from Oligocene age to less than 1.5 million years old. The area is part of a tectonic boundary between a volcanically active region north of the boundary and a less volcanically active region south of the boundary, which is also characterized by geographical differences, e.g. the presence