The 225 km2 dominantly andesitic Tenorio volcanic massif anchors the SE end of the Guanacaste Range and consists of a cluster of densely forested NNW-SSE-trending volcanic cones. Overlapping lava flows from the principal peak, Tenorio, cover the NW-to-SW flanks and descend the NE flank. The NW-most of three craters on the central cone is sparsely vegetated and appears to be the most recently active. Volcán Montezuma to the north has two craters, the northern of which was the source of a lava flow to the NE. Additional pyroclastic cones are found to the NE and SW of the central complex, and the Bijagua lava domes were constructed on the N flank. A major debris avalanche covered about 100 km2 below the S flank. A legend exists of an eruption in 1816 CE, but the volcano was densely forested at the time of an 1864 visit by Seebach and no documented eruptions are known. Fumarolic activity is present on the NE flank.