The Erie Canal's Unique Geological History

By Derrick Pratt, Erie Canal Museum Educator

A look at the unique geology that helped and hindered construction of New York’s Erie Canal


The story of the Erie Canal begins quite some time ago. About 480 million years ago to be exact, when the Appalachian Mountain range began forming. Over the next 200 million years, tectonic plates continued to collide along what is now the east coast of the United States. A great chain of mountains was formed, reaching heights comparable to the Rocky Mountains today and stretching from Georgia to Newfoundland.

As these mountains were rising, what is now upstate New York was covered by a shallow inland sea. Its life gradually accumulated on its floors, eventually compressing into the unique limestone that would be both a great help and hindrance to canal building efforts. When this sea dried up about 390 million years ago, the area around Syracuse came to acquire the salt deposits that made the city the great salt center of the Erie Canal. 

Over time, the towering heights of the Appalachian Mountains wore away, leaving behind the mountains we can see today, rising between 1,000 and 6,000 feet above sea level. While this was a considerable decrease in elevation, the Appalachians presented an almost insurmountable barrier to early European settlers.

There is, however, one gap in this ancient mountain range. This gap is the Mohawk River Valley and the plain of western New York. The Mohawk Valley formed about 13,000 to 11,000 years ago as the glaciers of the last ice age began to recede. The melt water from these glaciers collected into what is known as Great Lake Iroquois, as well as the other ancient Great Lakes. Today the remnants of Great Lake Iroquois form Lake Ontario and Oneida Lake. 

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Like Lake Ontario, Lake Iroquois drained the rest of the Great Lakes into the Atlantic. However, unlike Ontario, Lake Iroquois did not empty into the St. Lawrence River, as that was still covered in ice. Instead, it burst through the Appalachians forming the Mohawk and Hudson River Valleys. Eventually, the ice shelf receded far enough for the St. Lawrence to be uncovered and the drainage of the Great Lakes took its present form, but not before a great channel had been opened through the Appalachians. This opening was the key to the viability of the Erie Canal, and would also be a serious engineering challenge for early canal engineers.

The formation of the Mohawk River Valley was not the only important result of the last ice age when it comes to the geography that helped shape the Erie Canal. Just east of what is now Rochester, debris pushed by the glaciers accumulated into large ridges, forming what is today the Irondequoit Valley. These ridges were crucial in allowing the Canal to take the lower and more easily fed “Northern Route.” Their discovery by James Geddes in 1810 while surveying possible canal routes caused him to literally exclaim “Eureka,” according to his own recollections. 

One other glacial leftover was not so well received. That was what became known as “hardpan,” a dense mixture of clay, sand, gravel and stone that had been compressed by glaciers and was incredibly difficult to dig through. This soil would prove the ruin of a number of canal contractors, who found that their bids were too low to afford the added labor of clearing this unseen obstacle.  

All of these geological events were crucial in the development of the corridor we all know as the home to the Erie Canal. When you admire the Noses near Canajoharie or the Lockport locks cutting through the Niagara Escarpment, remember that this incredible canal is not just a wonder of human engineering but also a testament to millions of years of nature’s slow yet incredible power.