Madison Boulder Natural Area Maps

Madison Boulder Natural Area Description

Madison Boulder Natural Area is home to the largest known glacial erratic in North America, 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, 37 feet in width, and weighs upwards of 5,000 tons! The 17-acre site was acquired by the state of N.H. in 1946. In 1970 Madison Boulder was designated a National Natural Landmark by the U.S. Department of the Interior because the enormous erratic, "is an outstanding illustration of the power of an ice sheet to pluck out very large blocks of fractured bedrock and mov