Deerfield River Valley Mysteries: How the Glacier Age and other geologic events shaped the Deerfield River watershed For a fairly short river, the Deerfield exhibits quite a number of intriguing features that are commonly misunderstood or unexplained. The river starts in southern Vermont and runs 73 miles from to join the Conneccut River at the Deerfield - Greenfield border. Along the way the Deerfield traverses very different and dramac landscapes, all a heritage of our region's rich geologic history preserved in the underlying rocks. There are significant changes in geology along the way. Somemes the bedrock is hard metamorphic and igneous types, and in other places it is soſter sedimentary rocks like shale, sandstone, and conglomerate. In the hard rock areas, located upstream, the Deerfield Valley is narrow, a canyon even, with the river flowing within thousand foot high walls. This is just the place to create dams. Over the past 100 years 10 hydropower dams have been built. That's a dam every 7 miles on average, for its enre length, making the Deerfield River's water some of the most heavily used in the country. Farmland is what the lower Deerfield is most famous for. Here the valley is wide and flat with no stones of note, so the landscape really favors the plow. The underlying geology here is composed of the weak sedimentary "red rock" strata. These lowlands were eroded by glaciers and then covered by glacial Lake Hitchcock as the ice melted. The muddy and sandy deposits of the lake, as well as later river floodplain deposits, form the excellent terraced landscape that make up the Deerfield campus and surroundings and is the producve base for ferle soil development. Why are the Deerfield's valley shapes so different from upstream canyons to downstream floodplains? To solve this mystery, we need to view into the depths of geology me, back to the Paleozoic Era 500 million years ago. During the early Paleozoic North America's shoreline ended near the eastern New York border. Except for a thin strip of Vermont, New England was not even part of our connent. However, New England is coming! It's coming in several pieces, called exoc terranes. These terranes are big islands of Earth's crust that, through the process of plate tectonics, collide with North America, adding to its real estate. Each collision results in mountains, culminang with the impact of Africa and Europe which created the superconnent of Pangea. Bedrock was squeezed upward to form the Himalaya-sized Appalachian Mountains. The compression and heat of these orogenic events transforms our bedrock into metamorphic rock types such as gneiss, schist, slate, and marble. Subterranean zones that melted, cooled slowly to crystallize into granite. These are typically very hard rocks, resistant to erosion, and the landscape records their unwillingness to yield to the forces of degradaon by standing tall and steep. This is the origin of the V-shaped valley profiles of the Deerfield's upper valley. Before we get to the lower valley's flat landscapes, let's look at a prominent mystery that has capvated many: the Shelburne Falls "Glacial Potholes". These beauful rocky outcrops are nicely exposed due to a dam that diverts the Deerfield's water. Dozens of circular erosion features called potholes are