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 Madison Boulder Natural Area in Madison, New Hampshire. The boulder is a huge granite rock measuring 83 feet in length, 23 feet in height above the ground, and 37 feet 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.