snow accumulations can be mistaken for glaciers. Vegetation and fauna Due to the dry climate, the region is a desert with no vegetation occurring above elevation. However, lichens and mosses have been found at higher elevations and green growths have been reported from the summit region. , there were no reports of plants in the waterbodies on Ojos del Salado. Salt, acid and cold-tolerant bacteria have been recovered from sediments in the lakes on Ojos del Salado, consistent with microorganism samples from similar dry volcanic environments. A diverse flora and fauna has been described in the lower elevation regions south-southeast of Ojos del Salado. Birds such as ducks, flamingos and geese and mammals such as guanacos and vicuñas occur in the Santa Rosa-Maricunga-Negro Francisco region. Chinchillas and vicunas live in the valleys south of Ojos del Salado, and have drawn humans to the region. Earwigs have been observed at elevation. West of the volcano lies the Nevado Tres Cruces National Park and in 1991/1994 there were plans to make a national park on the Argentine side as well. , the establishment of a "zone of touristic interest" encompassing Ojos del Salado was under discussion in Chile. Eruption history Volcanic activity probably commenced 26 million, 3.3-1.5 million years ago or during the late Pleistocene. The 3.7±0.2 million years old Las Lozas Andesite may have been a precursor of Ojos del Salado. The oldest rocks of Ojos del Salado are 3.5-3.4 million years old dacites in the lower parts of the volcano. Argentine geological maps define a "Ojos del Salado basal complex", which consists of a number of Miocene volcanoes that have erupted andesite and dacite, partially in glacial environments. The volcano developed in two stages, with the more recent one grown on top of the older. A somma volcano structure may have formed during an eruption that generated the pumice deposits on the lower slopes of the volcano, and there are potential air fall deposits north of it. Ojos del Salado may or may not have produced pyroclastic flows; the neighbouring Nevado Tres Cruces 67,000 years ago produced extensive deposits on, around Ojos del Salado and in the valley between the two volcanoes; these were originally interpreted to have originated at Ojos del Salado. A pyroclastic flow erupted by Ojos del Salado descended the Cazadero valley and constitutes the "El Quemado Ignimbrite". Cerro Solo, whose emplacement was probably accompanied by intense