Payún Matrú is a shield volcano in the Reserva Provincial La Payunia of the Malargüe Department, south of the Mendoza Province in Argentina. It lies in the back-arc region of the Andean Volcanic Belt, and was formed by the subduction of the Nazca Plate beneath the South American Plate. Payún Matrú, along with the Llancanelo, Nevado and Salado Basin volcanic fields, form the Payenia province. It has been proposed as a World Heritage Site since 2011. Payún Matrú developed on sediment and volcanic rocks ageing from the Mesoproterozoic to the Tertiary periods. It consists of a large shield volcano capped by a caldera, formed during a major eruption between 168,000 and 82,000 years ago, a high compound volcano (known as Payun or Payun Liso), and two groups of scoria cones and lava flows. The Pleistocene Pampas Onduladas lava flow reaches a length of and is the world's longest Quaternary lava flow. Volcanic activity at Payún Matrú commenced during the Plio-Pleistocene period, and generated lava fields such as Pampas Onduladas, the Payún Matrú shield volcano and the Payun volcano. After the formation of the caldera, volcanism continued both within the caldera as lava domes and flows, and outside of it with the formation of scoria cones and lava flows east and especially west of Payún Matrú. Volcanic activity continued into the Holocene until about 515 years ago; oral tradition of local inhabitants contains references to earlier eruptions. Name In local dialect, the term Payún or Paium means "bearded", while the term Matru translates as "goat". The field is sometimes also known as Payenia. Geography and geomorphology Regional Payún Matrú lies in the Malargüe Department of the Mendoza Province, in Argentina. The area is inhospitable due to the lack of usable water and high elevation. Nevertheless, there are many paved roads such as National Route 40 which passes west of the field, and National Route 186 which runs around its northern and eastern parts. The volcano is within the Reserva Provincial La Payunia. Owing to the variety of volcanic landforms, the province was included in the 2010 Tentative List of UNESCO World Heritage Sites and a number of potential geosites have been identified at Payún Matrú itself. The active field is part of the backarc area of the Southern Volcanic Zone, a long volcanic arc and one of four eruptive belts in the Andes; the other three being the Northern Volcanic Zone,