All known outcrops of obsidian flows in the Cordillera Real (Ecuador) have been mapped and sampled to reconstruct their eruptive history using geological observations, age determinations, and trace element data. Our results bear also on the recognition of the sources of obsidian artifacts, used in pre-Columbian tools, and on the reconstruction of ancient trading patterns in Ecuador. Three obsidian flow groups were identified on the basis of flow structures and state of preservation. The groups are further defined by differences in radiometric age, fission-track measurements made at two laboratories (Pisa, Italy, and Campinas, Brazil), and different trace element patterns, determined by neutron activation analysis (Pavia, Italy). The oldest obsidian flows form the upper part of the Basal Volcanic Complex (BVC), the basement of Quaternary Ecuadorian stratovolcanoes. Their ages fix the upper limit of the BVC at 1.5 Ma, in the central Cordillera Real. The two more recent episodes of obsidian rhyolitic volcanism are date at ∼0.85 Ma and slightly less than 0.2 Ma, corresponding in age to the present volcanic arc. © 1993.61-22132Arias, Bernardes, Bigazzi, Bonadonna, Cesar, Hadler Neto, Lattes, Radi, Identificação de provenência de manufacturados de obsidiana através da datação com o método do traço de fissão (1986) Ciência e Cultura, 38, pp. 285-308Asaro, Michel, Burger, Chemical Source Groups in Ecuadorian Obsidian: Major Sources of Archaeological Obsidian and Provenance Assignment of Artifacts (1981) Lawrence Berkeley Laboratory Report LBL-13247, p. 27. , University of CaliforniaBarberi, Coltelli, Ferrara, Innocenti, Navarro, Santacroce, Plio-Quaternary volcanism in Ecuador (1988) Geological Magazine, 125 (1), pp. 1-14Bell, (1965) Investigaciones Arqueoógicas en el Sitio de El Inga, Ecuador, p. 330. , Editorial Casa de la Cultura Equatorian, Quito, EcuadorBigazzi, Oddone, Datazione dello standard internazionale apatite del Fish Canyon tuff [in Italian with English abstract] (1990) Rendiconti della Societá Geologica Italiana, 13, pp. 133-134Bigazzi, Marton, Norelli, Rozloznik, Fission-track dating of Carpathian obsidians and provenance identification (1990) Nuclear Tracks and Radiation Measurements, 17, pp. 391-396Bigazzi, Meloni, Oddone, Radi, Provenance studies of obsidian artifacts: trace elements analysis and data reduction (1986) Journal of Radioanalysis and Nuclear Chemistry, 98, pp. 353-363Dixon, (1990) BMDP Statistical Software Manual, p. 1385. , University of California Press, Los Angeles, CA, USAHenderson, (1984) Rare-Earth Elements Geochemistry, p. 510. , Elsevier, Amsterdam, The NetherlandsLynch, Pollock, La arqueología de la Cueva Negra de Chobshi (1981) Wis Med J, 1, pp. 92-119Manley, Fink, Internal texture of rhyolite flows as revealed by research drilling (1987) Geology, 15, pp. 549-552Mayer-Oakes, El Inga A Paleo-Indian Site in the Sierra of Northern Ecuador (1986) Transactions of the American Philosophical Society, 76, p. 235. , (Part 4)Miller, Wagner, Fission-track ages applied to obsidian artifacts from South America using the plateau-annealing and the track-size age-correction techniques (1981) Nuclear Tracks and Radiation Measurements, 5, pp. 147-156NIST Standard Reference Material Catalog, 1990–1991 [NIST Special Publication 260] (edited by R.L. McKenzie). National Institutes of Standards & Technology, Washington DC, USA, 161 pOsorio Araya, Datação de Obsidinas com o Métoto dos Traços de Fissão (1990) PhD thesis, p. 62. , Universidade Estadual de Campinas, Campinas SP, BrasilOsorio, Hadler, Bigazzi, Norelli, Coltelli, Salazar, Dados preliminares de idades de obsidianas do Ecuador pelo metodo dos traços de fissão (1991) Revista Brasileira de Geofisica, 9, pp. 55-59Salazar, El Intercambio de obsidiana en el Ecuador Precolombino: Perspectivas teórico-metodológicas (1992) Arqueologia en America Latina Hoy, , G. Politis, Biblioteca Banco Popular, Fondo de Promoción de la Cultura, Bogotá, ColombiaSaville, (1910) The Antiquities of Manabi, Ecuador: Final Report [Contributions to South AmericanArchaeology], p. 284. , The George G. Heye Foundation, New York, NY, USASimkin, Siebert, McClell, Bridge, Newhall, Latter, (1981) Volcanoes of the Workd [Smithsonian Institutions], p. 226. , Dowden, Hutchinson & Ross, Stroudsburg, PA., USAZeil, (1979) The Andes: A Geological Review, p. 117. , Gebrüder Borntraeger, Berlin, Germany