Coarse-grained aggregate deposited by a catastrophic flood located north of Fort McMurray, Alberta, was examined using ground-penetrating radar (GPR) and lithostratigraphic logging techniques. GPR transects were acquired from an upper scoured zone of flood deposits. Sedimentary structures (cross-beds and plane-beds) within the coarse sand and gravel and determinations of depth to bedrock (sediment thickness of the aggregate) were recognized in the GPR profiles by their varying dielectric properties. Fine-grained, conductive underlying oil-sand, till, or glaciolacustrine sediment (silt and clay) attenuated the radar signal. The sedimentary structures mapped from the GPR transects were confirmed in adjacent trench exposures. We suggest that GPR is an efficient methodology for determining volumes of aggregate reserves, thicknesses of aggregate deposits, and mapping sedimentary structures of high-energy fluvial sediments. Key words : aggregate, ground-penetrating radar, Alberta, spillway.