Strandplains of shore-parallel beach ridges bordering the Great Lakes are valuable for reconstructing histories of climate-related lake-level fluctuations. However, imprecise radiocarbon dates of ridge formation have frustrated development of dependable chronologies from which information about variation in the frequency of ridge formation and inferred climate fluctuations can be obtained. The resolution and precision of radiocarbon chronologies can be improved with AMS 14C dates of roots and rhizomes of plant species associated with the formation and growth of the sand-dune caps of beach ridges. These dates reliably estimate the timing of shore progradation when the base of the previously established beach ridge becomes inundated by the water table. An AMS radiocarbon chronology of beach-ridge formation in northern Lake Michigan shows that information about variation in the frequency of ridge formation is important for paleoclimatic interpretation.