Orosí is one of a cluster of four eroded and vegetated cones in the Guanacaste Range at the NW corner of Costa Rica. Volcán Orosí itself has a conical shape as viewed from the north or west, but its flanks are heavily eroded. The complex includes Orosí, Orosilito, Volcán Pedregal, and Cacao. The highest peak of the volcanic complex is 1659-m-high Volcán Cacao, 5.5 km SE of Orosí. The summit of Cacao is cut by two large horseshoe-shaped calderas breached to the SW and east related to edifice collapse. The age of the latest activity of the complex is not known. Historical eruptions were reported from Orosí in 1844 and 1849, but even at the time of the first volcanological observations at the end of the 19th century, Orosí was overgrown with large trees, and the eruptions may actually have been from neighboring Rincón de la Vieja. The latest documented volcanic activity produced mudflows (perhaps secondary) about 3500 years ago.