A major complex on the Chile/Argentina frontier, Cerro Falso Azufre is the main edifice of an elongate, arcuate complex extending about 15 km from west to east, Cordon Falso Azufre (Figure 41.1;41.2). The westernmost part of the complex is a crater chain 6–7 km long, composed of ~ 6 overlapping craters a few hundred meters in diameter. Activity may have migrated westwards along the chain because the westernmost crater is much the largest (1.5 km diameter) and most complete (Figure 41.3). Much of the activity from the craters appears to have been pyroclastic and the area proximal to the vent is blanketed with what may be a welded airfall deposit (Figure 41.3). While there are a number of extensive lava flows on both north and south flanks of the ridge, none seems particularly fresh, nor to be related to individual vents on the crater chain.