Maipo, a conical stratovolcano that straddles the Chile-Argentina border SE of Santiago, partially fills the 16 x 20 km Pleistocene Diamante caldera, which formed about 450,000 years ago during an eruption that produced an about 350 km3 of rhyolitic ignimbrite. The Pleistocene cones of Volcán Don Casimiro and Cerro Listado were formed on the SW rim and SW flank of the caldera, respectively. The post-caldera Maipo rises about 1,900 m above the caldera floor, and has several cones on the E flank along a series of en échelon NE-trending fractures. Lava flows from one of these cones blocked drainages in 1826 inside the caldera, forming Lake Diamante on the eastern caldera floor.