Cerro del Azufre is the largest and youngest volcanic center of a 50-km-long, NW-SE-trending chain of Chilean volcanoes just W of the Bolivian border, S of Salar de Ascotán. The northern summit forms the high point of the andesitic volcano; an older southern stratovolcano extends SE towards the Pleistocene Cerro Aguilucho volcano. A large group of late-Pleistocene lava flows originating from the northern cone extends toward the northern flanks and partially overlies a debris-avalanche deposit now largely buried by the Salar de Ascotán. The Chanka (Pabellón) dacitic lava-dome complex occupying the lower W flank is pristine-looking, but has been Potassium-Argon dated at 1.5 million years. Two possible Holocene dacitic lava domes that were erupted along a NW-SE line E of the summit ridge mark the most recent effusive activity, but two youthful-looking craters on the main edifice could be Holocene.