Roughly 14,000 years ago, New England was transitioning from ice age conditions (mile-thick ice overhead) to a climate more like today. You can image that melting a mile-thick ice sheet the size of Canada would be a bit messy, lots of water, lots of dirt melting out, lots of flooding. Image spring flooding times a billion and without vegetation. The Connecticut River Valley had a sediment dam at the southern end deposited by the ice sheet, so the valley was filled by a long, thin lake, called Glacial Lake Hitchcock, with the highest shoreline at ~650 feet above current sea level. If you are adventurous, you could see if these shoreline are on public property (like around Boston Lot), let me know what you find!