The Payún Matrú volcanic field in Argentina includes a massive hawaiian-style shield volcano that lies 530 km from the oceanic trench. The 8 x 10 km alkaline caldera of Cerro Payún Matrú was formed after about 168,000 years ago. The high point of the massif, Cerro Payen stratovolcano, was constructed on the SW flank of the shield. The Pleistocene Pampas Onduladas pahoehoe lava flow traveled 181 km, Earth's longest known Quaternary lava flow. Post-caldera basaltic eruptions produced more than 300 eruptive centers, mostly along E-W fissures that extend across the entire edifice. Fluid lava flows from a concentration of vents on the W flank known as Los Volcanes traveled more than 10 km. Other vent clusters of the 5,200 km2 volcanic field are found on the lower NE and S flanks, and a lava flow from Volcán Santa María on the NW flank traveled 15 km NE. At least 30 trachyandesitic lava domes and basaltic lava flows were erupted contemporaneously with the basaltic fissure eruptions. The Puente and Chapua volcanic units east of the main shield and south of the Ondulas flow are considered part of the field. Oral traditions note that indigenous tribes were present at the time of the latest eruption.