Madison Boulder Natural Area Off Route 113 Madison, NH 03849 Madison Boulder is the largest known erratic in New England, and among the largest in the world. Madison 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 this roughly rectangular block is buried, probably to a depth of ten to twelve feet.