Irondequoit Bay Geological History

There have been many glaciers that have designed the topography of Irondequoit Bay and surrounding land. The Wisconsin Glacier was last of the glaciers to pass through upstate New York. It extended as far as the Pennsylvania border and reached over a mile thick. The glacier retreated, scared and dumped as it traveled to the north, leaving behind a plethora of diverse, glacial deposits. The most common sediment in the area is sand—hence the sand cliffs visible on Irondequoit Bay. The glaciers also left behind a maze of land formations like the diverse, hilly terrain of the Irondequoit Creek watershed.

The massive melting glaciers flooded much of Monroe County, creating numerous lakes. One lake in particular, Geologist call Lake Iroquois. at the time, the lake level at the southern end was as high as Ridge Road. Today, Ridge Road lies on top of a bar developed by wave action from the lake. Along the ridge, and south of it, there are many areas of muck land where lake Iroquois use to exist (Please look at the arial map above to see how Lake Iroquois shaped the area North of Ridge Rd. ).

 
The Glaciers also rerouted the ancient Genesee River from the present day Irondequoit creek basin to what is now Charlotte. It flowed into the lake carrying large amounts of silt and formed a delta. Today the Town of Irondequoit covers much of this delta.

At the south end of Irondequoit Bay, there was a long narrow bay that extended southward as far as East Rochester. Streams carried material into this bay, which was sorted by wave action, gradually filling the bay. The bay itself occupied a valley cut long before the ice age by a northward flowing stream which drained the same general area as the present day Genesee River. For this reason, the bay is said to occupy part of the valley of the pre-glacial Genesee. Irondequoit Creek cut a channel through this filling the lake with sand.