Palaeoecological investigations were carried out at a late Bronze Age site situated at Carrownaglogh, northeast Co. Mayo, with a view to reconstructing environmental conditions prior to and following blanket bog growth, which served to preserve the site.The main feature of the excavated area consisted of a stone wall enclosure (2.2 ha) sited on a small knoll at 150 m O.D. Well defined cultivation ridges, 14C dated to the 9th century B.C., filled the area within the enclosure. Outside the enclosure, the ground is ridged or levelled and stone cleared.Soil profile descriptions, chemical and mechanical analyses of fossil soils and pollen analysis of a series of short monoliths, which included mineral soil and overlying peat, were carried out.To facilitate interpretation of the pollen analytical results surface samples from poorly fertilised arable land, where chemical weed control was minimal, were pollen analytically investigated.A pollen diagram from the adjoining basin, spanning the period from c. 3600 yr B.P. to recent times, enables results of the above investigations to be placed in the context of the regional vegetational history.Three distinct phases of extensive woodland clearance associated with arable and pastural farming are identified, dating to 2750, 1950 and 1000 yr B.P. The first of these, which emerges with particular clarity in the concentration pollen diagram, is equated with the farming phase which resulted in the ridge formation on the knoll.