The Taconic Mountains are a 150-mile-long sub-range of the Appalachian Mountains lying on the eastern border of New York State and adjacent New England. The range, which played a role in the history of geological science, is separated from the Berkshires and Green Mountains to the east by a series of valleys, principally those of the Housatonic River, …The Taconic Mountains are a 150-mile-long sub-range of the Appalachian Mountains lying on the eastern border of New York State and adjacent New England. The range, which played a role in the history of geological science, is separated from the Berkshires and Green Mountains to the east by a series of valleys, principally those of the Housatonic River, Battenkill River and Otter Creek. The Taconics' highest point is Mount Equinox in Vermont at 3,840 feet ; among many other summits are Dorset Mountain, Mount Greylock and Mount Everett.