One of the tectonic terranes that make up Connecticut. Terrane boundary defined using the CT GIS Bedrock Geology Map from the CT DEEP. Elevation data from the 1/3 arcsec digital elevation model downloaded from the USGS National Map.
"Hole" in the terrane reflects the location of the Willimantic Dome, part of the Avalonian terrane, poking through the younger rocks of the Merrimack.