Your geologic walking tour of Turners Falls begins at the three-dimensional model in the lobby of the Great Falls Discovery Center, an interpretive museum of the Connecticut River watershed. A watershed is an area drained by a river.
The Great Falls Discovery Center is a Massachusetts Department of Conservation and Recreation visitor center that celebrates the natural, cultural, and industrial history of the Connecticut River Watershed with support from the Friends of the Great Falls Discovery Center.
THINGS TO SEE
Valleys old and new. A prominent feature of the watershed model is the Connecticut River Valley, a remnant of that great rift valley that once spanned Pangea over 245 million years ago. Looking at the model, you’ll see that the modern-day valley extends geographically from the northern tip of New Hampshire to Long Island Sound.
Pangea breaks apart and the land changes. The heating of rock deep within the Earth caused tremendous geologic forces that pulled Pangea apart. Those forces produced the depositional environment that formed the valley now cradling the Connecticut River. (A depositional environment is one in which sediments settle out of water.)
Prodded loose by water and perhaps earthquakes, rock and sediment from ancient highlands to the west and east began to pour into the rift valley. As the valley sank under this heavy load, the surrounding highlands regained their relative elevation. This, in turn, resulted in more erosion and sediment buildup. This process went on for tens of millions of years.
THINGS TO KNOW
Valley sinks down, sediments pile up. As the heavy sediments sank, the southeastern flank of the valley slipped deeper than the northwestern flank. Sediment gradually filled the valley in overlapping deposits called alluvial fans. Eventually, the sediment filling the valley reached a thickness of up to 6,500 feet and, under the pressure of burial, turned to rock. Today, these southeastern-dipping rocks (called the Turners Falls “red beds”) form sandstone ridges that extend through Turners Falls and Montague until they disappear underground near the Montague/Sunderland town line.
Rifting helped the river grow. The pulling apart of Pangea caused long north-south cracks to form in the ancient rocks that underlie the valley. Over millions of years, those north-south cracks enabled the development of the Connecticut River, which forms the border between New Hampshire and Vermont as it flows south through the valley, from the New Hampshire/Quebec border to the Atlantic Ocean via Long Island Sound.
A hard right turn. Notice on the model how the river turns abruptly east at Middletown, Connecticut, before heading south to tumble into the Atlantic at Old Saybrook. The river takes that sudden turn because the basalt (or cooled lava) rock ridges west of the river–a remnant from the violent volcanic break up of Pangea–are too hard for the river to break through.
NEXT STOP
Step outside the Discovery Center lobby, head down the driveway that runs alongside the Great Hall as you face the building, and continue toward the footbridge over the Power Canal. Cross the footbridge and walk to the grassy area under the power lines overlooking the river.
