Ever wonder about the geology of the Mohawk Valley in our area? What formed the cliffs that gave Clifton Park its name? Why is the valley so narrow where the I-87 Northway bridges the Mohawk? How old is the Cohoes Falls?
The most concise answer I have read is from the draft Mohawk River Basin Action Agenda published by NYSDEC, “Glacial ice and meltwater played a major role in the geologic and landform development of the Mohawk Valley. Prior to the last glaciation, the Mohawk drained south from Schenectady and joined the Hudson River near Coeymans, NY. Following glaciation, this route was buried by glacial sediments and a much larger ‘Iromohawk’ river drained through the valley. For a period of a few hundred years, while the St. Lawrence Lowland was blocked with ice, the Iromohawk conveyed the drainage of the Great Lakes and the meltwater of the eastern Laurentide ice sheet through the valley. The Iromohawk cut wide channels across the Hudson-Mohawk Lowland, deposited cobble-sized gravels in many locations east of Little Falls, and eroded bedrock between Rexford and Cohoes, forming the route the modern river follows today.”
A more detailed discussion of the glacial retreat and the sequence that shaped the Mohawk Valley is contained in a more detailed blog with some well done maps.
I also understand that the very hard basalt geology over which the Mohawk River Falls at Cohoes is one of the youngest, surficial geological formations within what we now call New York State.