Monument Mountain is the name of a popular 503-acre (204 ha) open space reservation located in Great Barrington, Massachusetts on the southeast side of Monument Mountain. The reservation is centered on the 1,642 feet (500 m) subordinate summit of Squaw Peak. It is managed by The Trustees of Reservations, a non-profit conservation organization and is notable for its expansive views of the Housatonic River Valley, The Berkshires, the Taconic Mountains, and the Catskill Mountains of New York from the knife-edge summit of Squaw Peak. Monument Mountain, composed of erosion resistant quartzite, is of The Berkshires geology. The reservation receives over 20,000 visitors a year.