Presque Isle is a recurved sand spit that formed during the last glacial period, or ice age, when the Laurentide Ice Sheet advanced into the basin now occupied by Lake Erie, and, when it retreated to the north between 12,370 BC and 12,790 BC, left behind a moraine consisting of clay, sand, and gravel that initially formed the Presque Isle peninsula. The deposits are constantly being re-worked by wave action and are gradually migrating to the northeast due to longshore drift.