Washington County, New York is part of the Great Appalachian Valley (also known simply as the 'Great Valley') which is a long narrow valley strip often between tall mountain ranges. The county transitions from the Taconic Mountains to the Adirondack Mountains, and from the Lake Champlain Valley to Hudson River Valley. Much of the county is part of the slate valley of the Upper Taconic Mountains (Taghkanic, meaning 'in the trees'). The eastern boundary of Washington County is the New York–Vermont border, part of which is Lake Champlain. This is also the border with New England proper. The northern end of the county is
Rock River (Lake Champlain) Rock River (Lake Champlain) The Rock River is a short tributary of Lake Champlain in northern Vermont in the United States and southern Quebec in Canada. Via Lake Champlain and the Richelieu River, it is part of the watershed of the St. Lawrence River. According to the Geographic Names Information System, it is also known as "River Rocher" and "Riviere de La Roche." The Rock River flows for most of its length in Franklin County, Vermont, rising in the town of Franklin and flowing eastwardly into the town of Highgate, where it turns northwardly and briefly flows for a short