Palaeoenvironmental investigations not only provide information about past climate, geomorphological changes, and vegetation, but also can give a unique and complementary perspective to archaeological studies relating to the history of human settlement. The IARII Laguas core on the west coast of Guam yielded 28 meters of sedimentary deposition dating back 9,300 years from the present. Pollen analysis indicates that forested conditions dominated the upland and coastal landscape of southern Guam during the early part of the Holocene. At 4,300 cal. B.P. the earliest charcoal particles appear, suggesting human colonization. By about 3,900 cal. B.P. Lycopodium and Gleichenia ferns first become noticeable in the core record, probably indicative of gardening and resource collecting activities by small human populations. At 2,900 cal. B.P. these and other disturbance indicators (e.g., grasses, charcoal articles) become continuously present in quantity, signalling the demise of the upland forests in southern Guam and development of the degraded savanna landscape seen today. By 2,300 cal. B.P. there are only remnant patches of native forest in evidence. The sedimentary record of the Laguas core and another nearby sampling location suggest increased hillslope erosion along the coastal margins after about 1,700 cal. B.P., which is accompanied by higher charcoal particle concentrations. Although the exact date of major coastal deposition remains unresolved by the Laguas evidence—it could have been much later than 1,700 cal. B.P.—other studies of erosion and coastal deposition on Guam suggest a time frame sometime between the early first millennium B.P. and late second millennium B.P.