Cornish lies within the Connecticut River Basin, the largest watershed in New England. The basin was formed through mountain building and erosion over millennia, but our current-day landscape was formed 10,000-14,000 years ago by glacial forces. The Connecticut River Valley is the former Glacial Lake Hitchcock, which extended from a natural dam in Rocky Hill, CT northward to St Johnsbury, VT.

On the higher terrain the glaciers eroded away the surface of the region’s hills and mountains to expose the underlying bedrock, outcrops we call ledge. The overlying material was mixed into the glacial ice and carried along as the glaciers moved southward. When the climate warmed and the glaciers retreated in our River Valley, they dropped their load of boulders, gravels, sand, silts and clay that we see today. This resulted in a geology in Cornish that is largely glacial till on top of bedrock. And we wonder why gardening and farming can be so challenging in the Cornish hills!!!! Also known as New England Uplands, the topography of Cornish is underlain by granite, gneiss, schist, slates and shales. This results in soil that is predominantly stony or very stony sandy loams to loams with minimal silt or clay present. Soils are very acidic and also quite shallow, making them often unsuitable for homesites or septic tanks and fields!

About 12,000 years ago, the dam at Rocky Hill broke, and Lake Hitchcock drained into what is now the Connecticut River. Seasonal floods deposited rich alluvial sediments over the ensuing period resulting in prime farmland, found in Cornish along the eastern bank of the river. Separately there is also some prime farmland along the Route 120 corridor in Cornish and smaller areas of suitable farming land scattered throughout the central portion of Town. The glacial forces of millenia have truly influenced what the human inhabitants of Cornish have been able to create ever since the glacial retreat!