46°50′50″S 75°20′04″W / 46.84722°S 75.33444°W
The Tres Montes Peninsula (Spanish: Península Tres Montes, English: Three Hills Peninsula) is a southwestward projection of Taitao Peninsula which in turn connects to the mainland of Chile by the narrow Isthmus of Ofqui. The peninsula is situated in Aysén del General Carlos Ibáñez del Campo Region close to the Chile Triple Junction of the Nazca, Antarctic and South American plates.
The Chile triple junction (or Chile margin triple junction) is a geologic triple junction located on the seafloor of the Pacific Ocean off Taitao and Tres Montes Peninsula on the southern coast of Chile. Here three tectonic plates meet: the South American plate, the Nazca plate and the Antarctic plate. This triple junction is unusual in that it consists of a mid-oceanic ridge, the Chile Rise, being subducted under the South American plate at the Peru–Chile Trench. The Chile triple junction is the boundary between the Chilean Rise and the Chilean margin, where the Nazca, Antarctic, and South American plates meet at the trench.
The South American plate is a major tectonic plate which includes the continent of South America as well as a sizable region of the Atlantic Ocean seabed extending eastward to the African plate, with which it forms the southern part of the Mid-Atlantic Ridge.
The easterly edge is a divergent boundary with the African plate; the southerly edge is a complex boundary with the Antarctic plate, the Scotia plate, and the Sandwich Plate; the westerly edge is a convergent boundary with the subducting Nazca plate; and the northerly edge is a boundary with the Caribbean plate and the oceanic crust of the North American plate. At the Chile triple junction, near the west coast of the Taitao–Tres Montes Peninsula, an oceanic ridge known as the Chile Rise is actively subducting under the South American plate.
The Taitao Peninsula (Spanish: Península de Taitao) is a westward-facing landmass on the south-central Pacific west coast of Chile. The peninsula is connected to the mainland via the narrow Isthmus of Ofqui, over which tribal peoples and early missionaries often traveled to avoid navigating the peninsula's treacherous waters, carrying their boats and belongings overland between the Moraleda Channel and Gulf of Penas. The Taitao Peninsula is situated in the Aysén del General Carlos Ibáñez del Campo Region, and part of the landmass is located inside the boundaries of Laguna San Rafael National Park. The Presidente Ríos Lake, with a surface area of 352 square kilometres (136 sq mi), lies in the center of the peninsula. A southward-incurving projection of its outer shoreline is known as Tres Montes peninsula, the most southerly point of the cape of the same name.
Spanish explorers and Jesuits that sailed south from Chiloé Archipelago in the 17th and 18th centuries regularly avoided rounding Taitao Peninsula entering instead the Gulf of Penas after a brief land crossing at the isthmus of Ofqui. While attempting to pass the Gulf of Penas in 1741, a storm caught the British ship, HMS Wager, causing it to wreck on (the eventual) Wager Island, on the Guayaneco Archipelago. Some of the survivors, including John Byron, were led into the Spanish settlements of the Chiloé Archipelago by the Chono chieftain Martín Olleta via Presidente Ríos Lake.