A continuing study of the sand body developed long the eastern shore of Lake Ontario (NY) sponsored by The Nature Conservancy, has revealed a complex post-glacial lacustrine and shoreline stratigraphy. Offshore sand sheets, up to a few meters thick and extending over 25 km along the barrier-beach dominated coast, are separated by erosion surfaces observed both on high-resolution seismic-reflection records and in vibracores. Deposits of former shorelines at depths as much as 20 m below present indicate episodes of highly variable lake level and change to a more arid climate. A major purpose of the study is to determine the origin, modern mobility and fate (erosion and deposition) of the fine sand and gravel seen along the shore and of the fine sand seen in the dunes back of the shore. Understanding any exchange between the shore and offshore sand reservoirs may be critical to land management planning for the study area. Shore and dune sands have been sampled with vibracore to a depth below the surface of a few meters. Associated internal structure of the sand has been revealed in high-resolution, ground-penetrating radar (GPR) data collected along six representative transects run between the lake and back-barrier ponds. As with the offshore sands, it is apparent that the stratigraphy of the shore and dune sand is most readily explained in terms of lake level change. Also recognizable are cut and fill features caused by barrier inlet relocations and normal beach and dune cycles of development. Erosional or non-deposition surfaces subdivide the beach and dune sands into units no more than a few meters thick. Accretion-surface bedding is apparent in the beach, the dunes and the filled inlet-channel features cut into the older barrier-beach and wetland sediments seen below the dunes. Evaluation of the internal structures of the shore and dune sands has revealed a more complex stratigraphic development than previously modeled. C14 dates of the organic plant material collected in the vibracores will make it possible to calibrate the shore and dune accumulation rates and correlate it with the now submerged and buried shoreline stratigraphy discovered below the offshore sand sheets.