ABSTRACT Ground penetrating RADAR was used in an attempt to map sediment accumulation in active and abandoned beaver {Castor canadensis) ponds in northern Minnesota and to map buried paleochannels of the Flathead River floodplain in Montana. We attempted to map ice thickness, water depth, sediment depth, depth to parent material (bedrock or clay), thickness of soil horizons, organic deposits (peat), frost penetration, and depth to the water table in the beaver ponds. Ground penetrating RADAR successfully located some of the subsurface interfaces between these layers but water saturation and the high clay content of the soils interfered with the ground penetrating RADAR signal while the physical complexity of the subsurface hampered data interpretation. In Montana, paleochannels and water tables were located, but the stony nature of the substrate prevented immediate excavation for verification. In both Montana and Minnesota, success depended strongly on physical characteristics of the sites and specific interfaces. Generally, our efforts were only successful where the physical subsurface interfaces had abrupt, well defined boundaries, and where clay content was low.