Erie Plain  The Erie Plain is a lacustrine plain that borders Lake Erie in North America. From Buffalo, New York, to Cleveland, Ohio, it is quite narrow (at best only a few miles/kilometers wide), but broadens considerably from Cleveland around Lake Erie to Southern Ontario, where it forms most of the Ontario peninsula. The Erie Plain was used in the United States as a natural gateway to the North American interior, and in both the United States and Canada the plain is heavily populated and provides very fertile agricultural land. The Erie Plain is a lacustrine plain consisting largely of sediment laid down by a series of proglacial lakes. These existed in the late Pleistocene Epoch, about 25,000 years ago to about 11,700 years ago, and were created by glaciers of the Wisconsin glaciation (the last ice age). The largest of these was Lake Whittlesey. In some places in Pennsylvania and Ohio, the Erie Plain is broken by the very slight former shoreline of Lake Warren. This glacial sediment was laid atop the Chagrin and the Cleveland shales created in the late Devonian Period (382.5 to 359 million years ago), as well as early Carboniferous Period shale in and west of Cleveland (laid down 359 to 346 million years ago). West of Sandusky, Ohio, these sediments lie atop limestone laid down in the Silurian and Devonian periods. Due to its lacustrine origin, much of the soil of the Erie Plain contains abundant clay, although in some areas it is quiet sandy where ancient beaches formed. Beneath this relatively thin layer of soil is unconsolidated moraine, soil and rock left behind as the glaciers retreated. Three geologically distinct plains border Lake Erie. The lowest of these is the Ontario Plain, followed by the Huron Plain and then the Erie Plain. Escarpments separate the plains from one another. Between the Erie Plain and the Appalachian Plateau is the Portage Escarpment. The Erie Plain begins just east of Auburn, New York, where the Onondaga Escarpment meets the Portage Escarpment. The Onondaga Escarpment sharply distinguishes the Erie Plain from the Huron Plain east of Buffalo. But along the southern side of Lake Erie west of Buffalo, the Onondaga Escarpment is so slight that the Huron Plain and Erie Plain are essentially the same. At Buffalo, the plain narrows to just wide as the Portage Escarpment moves closer to the Lake Erie shoreline, and remains wide in Erie County, Pennsylvania.