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This paper summarizes the results of on-going archaeological and palaeoecological research on the floodplain of the river Cauca and adjacent piedmont, with the aim of reconstructing an outline history of the human occupation of the region and its interaction with the environment, beginning in the Late Pleistocene. The difficulties of locating occupation sites in this landscape cannot be overestimated. Although valuable for its preservation of palaeosols, the accumulation of sediment deposited by the river Cauca and its tributaries during periods of flooding can be extremely rapid and the earlier archaeological sites (1000 B.C. to 500 A.D.) are generally buried beneath several metres of alluvium. Under these circumstances, traditional site survey has limited potential and the most promising strategy is the location of palaeosols with evidence of human activity based on soil analysis and palaeobotanical studies.

Sedimentology from a dozen deep cores is providing invaluable information on the environments that early human populations in the area would have enjoyed or coped with. The cores testify to a highly dynamic river Cauca and its tributaries resulting in a series of rapid local environmental changes. Besides extensive periodic flooding, past populations were probably affected by tectonic events since numerous faults cross the region. Volcanic ash is a component of many of the soil cores but much was redeposited material from earlier falls, probably during the Pleistocene.

Direct archaeological evidence of human activity during the Early and Middle Holocene is limited to a mastodon skeleton with butchering marks on its ribs, and to a surface find of a stone tool (azada) characteristic of this period. Of the numerous fertile palaeosols detected in cores, some have agricultural characteristics and there is evidence of fires, possibly for clearing fields, from the late seventh millennium B.C. while by the third millennium B.C. a site provides evidence of burning in combination with the cultivation of maize (Zea mays) and arrowroot (Maranta arundinacea).

While a relatively large number of archaeological sites testify to human activity over much of southwestern Colombia during the Early and Middle Holocene, research has drawn attention to a period of archaeological silence between 2500 and 1000 B.C. when Formative societies were developing in other regions of South America. An important focus of this project is the search for traces of human activity during this period. The palaeosols have important potential for acquiring information on this question since stratigraphical evidence suggests that many lie within this time range. By the Late Holocene (c. 500 B.C.) the Ilama population was established in that region of the alluvial valley centred on Lake Sonso and the town of Palmira, followed by Yotoco and, further south, Malagana; in contrast, in the northern sector of the valley evidence for this sequence remains tentative. Here the only settlement site located so far with very late Formative characteristics produced an entirely new style of pottery. This site (first century B.C.) was in wooded marshland where houses must have been built on stilts, contrasting with Late Period sites (c. AD 500-1500), occupied by a sequence of different cultural groups of the Sonsoide tradition and located on slightly higher ground within the flood plain or in the piedmont.