During the last Ice Age, meltwaters that were impounded between a wall of glacial ice to the north, and the glacially deposited Fort Wayne End Moraine to the south, formed an enormous glacial lake well above the present level of modern Lake Erie. At that time, lake waters covered much of what is now Northwestern Ohio. Then, about 14,000 years ago, the Wisconsian Glacier, the last of four continental glaciers to spread across Ohio, made its final retreat northward freeing up the Niagara Outlet. Lake levels dropped rapidly exposing lake bottom across most of the northwest corner of the state, and eastward along a narrow strip paralleling but inland from the current Lake Erie shoreline. Drainage is therefore extremely poor throughout this Lake Plain Region due to the flatness of the landscape and the impervious clay soils that lined the glacial lake basin.
When lake levels dropped, fine yellowish sands, that had washed into the lake from what is now Michigan and deposited along the shoreline, were left inland high and dry to be redistributed across the land by wind. The most extensive of these deposits occurs in Northwestern Ohio covering an area of more than 150 square miles known as the Oak Openings. This is an area of sand barrens prairies, sand dunes, woodlands of widely spaced stunted oaks for which the region was named, and wet sedge meadows. Due to this variety of ecological communities, more state listed rare species of plants occur in the Oak Openings than anywhere else in the state.
Outside of the Oak Openings but within the Lake Plain, where the bed of the former glacial lake was now exposed, flooded most of the year, and based on a deep layer of mud, an extensive swamp forest became established. Later, this area of about 1,500 square miles became known as the Great Black Swamp. This was Ohio’s last wilderness until it was drained by the end of the 1800’s and converted into some of Ohio’s richest farmland.
Surrounding the shallow western basin of modern Lake Erie, vast marshes of Western Lake Erie and Sandusky Bay developed along with their own characteristic plant communities and special wetland wildlife. Two other special features of the Lake Plain include the Alvar Communities of the Marblehead Peninsula and Kellys Island, along with its famous glacial striations and grooves, and the well developed sand beaches at the eastern end of the Lake Erie Basin. These beaches are well known for the interesting Atlantic shoreline plants that migrated westward shortly after the glacier melted. The weight of the glacier had so compressed the bedrock that the Atlantic Ocean then extended into the present basin of Lake Ontario forming a corridor for the westward migrations of Atlantic coastal plants. Eventually, with crustal rebound of the compressed bedrock and the subsequent retreat of the ocean, these species became isolated from their Atlantic Coastal Plain origin.