The west slope of Alander Mountain is located within Copake, New York. The point where the state line crosses the ridge next to the South Taconic Trail is, at , the highest elevation in Columbia County. The summit and east side is within the town of Mount Washington, Massachusetts. The west side of Alander Mountain drains into the Preachy Hill Brook, then into the Noster Kill, Bash Bish Brook, the Roeliff Jansen Kill, thence the Hudson River and Long Island Sound. The east side drains into Ashley Hill Brook, then Bash Bish Brook and the Roeliff Jansen Kill.