The relentless rain across northern Ohio and yesterday's visit to the West Branch of the Mahoning River, prompted me to look once again at Ohio's portion of the Eastern Continental Divide. That line of "high ground," separating rivers that flow to the Atlantic from those that flow toward the Gulf of Mexico, enters western Ohio just north of Grand Lake; the divide then makes a curve to the south, cutting across that lake and dipping toward Lake Loramie, following the southern margin of the Maumee River watershed (and the northern edge of the Great Miami watershed).
From this area, the Ohio Divide makes an irregular, staircase-like march to the northeast corner of the State. En route, it separates the watersheds of the Maumee, Sandusky, Huron, Vermillion, Black, Rocky, Cuyahoga, Grand and Ashtabula Rivers to its north from those of the Great Miami, Scioto, Muskingum, Mahoning and Shenango Rivers to its south (west to east).
The Ohio Divide, rather subtle in most areas, reflects the effect of the Wisconsin Glaciation (the last of the Pleistocene, 70-10 thousand years ago) on the landscape of the Great Lakes Region, including northern Ohio. While the Wisconsin Ice Sheet pushed farther south than the current divide (especially in western Ohio), it sculpted the landscape by scouring the bedrock, spreading glacial till, depositing moraines, producing meltwater lakes, calving chunks of ice (see Kettle Lakes) and eroding post-glacial stream beds with torrents of meltwater. In addition, as the glaciers retreated into Canada, the land rebounded from their weight and the St. Lawrence Seaway opened, draining the swollen ancestors of today's Great Lakes. Of course, erosion continues today and the route of Ohio's Divide will shift over time.
