The Hilltown-Berkshire upland ends at the valley of the Housatonic River which flows south to Long Island Sound, and in the extreme north west of Massachusetts at the Hoosic River, a tributary of the Hudson. From these valleys, uplands to the east appear as a rounded mountain range, rising some 1,600 feet (500 meters) although they are actually a plateau. West of the Housatonic-Hoosic valley system rises the narrower Taconic Range along the New York border. Upper tributaries of the Hoosic separate Massachusetts' highest peak, Mount Greylock 3,491′ (1,064 meters) from both ranges, however Greylock's geology connects it with the Taconics.