The Madison Boulder is one of the largest known glacial erratics in North America and among the largest in the world; it is preserved in the 17-acre (6.9 ha) Madison Boulder Natural Area in Madison, New Hampshire. The boulder is a huge granite rock measuring 83 feet (25 m) in length, 23 feet (7.0 m) in height above the ground, and 37 feet (11 m) in width. It weighs upwards of 5,000 tons. A part of the block is buried, probably to a depth of ten to twelve feet. It was acquired by the state from the Kennett family In 1946. In 1970, Madison Boulder was designated as a National Natural Landmark by the National Park Service.