Ground penetrating radar (GPR) records of groundwater surface (GWS) reflections have been analyzed from 40 across-barrier profiles, totaling 50 km in combined length, taken from barrier spits and beach plains of the Columbia River littoral system. The barriers and beach plains host shallow fresh-water aquifers in the prograded beach deposits and abandoned foredune ridges, totaling 10–30 m in thickness. Study results demonstrate that GWS reflections could be traced continuously at subsurface depths of 1–15 m with the GPR 100 MHz and 50 MHz antennae using 400 V and 1000 V transmitters. Boreholes (62 in number) and lake water levels (24...