Cliff Mountain is an Adirondack peak in Essex County, New York, part of the Marcy Group in the Great Range and within the High Peaks Wilderness Area of Adirondack State Park. Its slopes feed the Opalescent River watershed, with water ultimately reaching the Hudson River and New York Bay. The mountain holds a distinctive place in Adirondack hiking history as one of the original forty-six High Peaks. Although a later U.S. Geological Survey found it to be under four thousand feet, the traditional list remained unchanged. With no marked trail to its summit, Cliff Mountain has kept a reputation as a remote and enduring objective for Adirondack hikers.