The types and spatial distribution of subsurface sedimentary deposits in the Calumet and Toleston Beaches of ancestral Lake Michigan were studied to better understand the evolution of the southeastern shore of Lake Michigan. Deposits of eight depositional environments were recognized: (1) dune, (2) foreshore, (3) upper shoreface, (4) lower shoreface, (5) offshore, (6) back-barrier lacustrine, (7) paludal, and (8) glacigenic.

The Calumet Beach formed at the end of a rise in lake level following the Two Creeks phase, a time period of low lake level in the Lake Michigan basin, to the Calumet level. This trasgressive event was primarily erosional...