Dating of five widely spaced (noncoastal) dunes in eastern upper Michigan by optically stimulated luminescence of quartz establishes that eolian sand was last mobilized between ca. 7 and 5.5 ka in the region. Although this interval corresponds to the drier Altithermal-Hypsithermal period, climate alone may not have been sufficiently and to cause dune formation in this area. Instead, it appears that dune formation may also be linked to depressed water tables, associated with outlet-controlled low levels in Lakes Michigan and Superior. Following dune stabilization, peat began to accumulate in interdune areas ca. 4.4 ka.