Late Pleistocene/early Holocene Tropical Forest Occupations at San Isidro and Pena Roja, Colombia

Article excerpt

Northern South America is not a homogeneous geographical area. The Ecuadorian Andes form a continuous, although diverse, mountain chain (with high inner valleys, jalcas and paramos), flanked in both sides by lowlands covered with rain forests. In southwestern Colombia the Andes split into three branches of different geological origin, forming interandean valleys much wider than the narrow valleys of the Central Andes and even Ecuador. Between the three cordilleras there are two low river valleys, the Magdalena and the Cauca. On both sides, as in Ecuador, there are lowland areas covered with tropical rain forests: the narrow Pacific strip and the Amazon Basin. To the north of the latter extend large plains covered with grasses, forested along the rivers. The rest of the area is made up of rolling savannas along the Colombia Caribbean and the arid strip of the Atlantic coast of Venezuela. These geographical variants on the Equator produce dramatic climatic changes along the altitudinal gradient. And the differences of insolation and solar exposure, of rainfall, and of soils, make a mosaic of markedly different and narrow tiers, except in the Amazon and the Eastern Plains where the ecosystems are substantially wider.

The available archaeological evidence indicates that humans occupied most of these varied ecosystems of northern South America by late Pleistocene/early Holocene times with a diverse stylistic and technological repertoire. In fact, hunter-gatherers were exploiting open areas [ILLUSTRATION FOR FIGURE 1 OMITTED] in the arid coast of Venezuela (e.g. Ochsenius & Gruhn 1979; Jaimes 1994); in the Orinoco river basin (Barse 1990); and in the semi-arid Magdalena valley (Lopez 1995). Evidence for human occupation of diverse tropical forests is better and well-organized in some regional sequences, and yet more abundant in high mountain forests, such as the Sabana de Bogota (e.g. Correal 1986), and the upper and middle Calima valley (Cardale 1992). Although there is sparse evidence indicating that the tropical lowlands may have been occupied since the late Pleistocene (Correal 1977; Reichel-Dolmatoff 1987: 47), good information of occupations dating to 9000 BP has been obtained only recently from a terrace of the Caqueta river in the Colombian Amazon (Cavelier et al. 1995). There a pre-ceramic occupation occurs in a tropical rain forest with unifacial tools and the exploitation of vegetal resources with grinding artefacts. This evidence is presented in this paper, along with new evidence of late Pleistocene hunter-gatherer adaptations to a tropical mountain forest in the valley of Popayan, in southwestern Colombia, where bifacial, unifacial and grinding tools have been uncovered along with abundant charred vegetal material.

San Isidro, in the valley of Popayan

San Isidro is located in an interandean valley, about 50 km northwest of the modern city of Popayan, in southwestern Colombia [ILLUSTRATION FOR FIGURE 1 OMITTED]. The archaeological site lies in the open on the flat summit of a small hill, 1690 m above sea level. Although most of the area around the site was cleared long ago, remnants of original vegetation correspond to subandean forest (sensu Cuatrecasas 1958). Modern annual rainfall is 1800 mm; it must have been substantially higher in the past under forest cover. A single preceramic component at the site covers approximately 60 sq. m; 20 sq. m, some 30% percent of the areal extension of the deposit, were excavated in 1993 using 1x1-m units and controlled by 5-cm levels. Soil was screened with a 5-mm mesh; 6 litres of sediments from each level were saved for flotation.

The archaeological deposit has a thickness of 40 cm (from 20 to 60 cm below the surface), with cultural material sparsely scattered between 5 and 85 cm below surface. The largest concentration is in a thickness of some 5 cm at an average 40 cm below surface; this suggests that the site was formed by a relatively short occupational event. …