Madison Boulder Natural AreaApril 19. 2011 9:17PM
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.
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 move them substantial distances."
Location: Off Route 113, Madison
Operation Schedule: Mid-May to Mid-November
Acreage: 17 acres
How did it get here?
Madison Boulder is made of fine-grained feldspar and larger quartz crystals that welled up under great pressures from a molten mass deep in the earth over 200 million years ago. Upon cooling, the molten rock hardened. Over the millions of intervening years softer materials on the earth's surface were removed by erosion from wind and water. Not so with the granite of New Hampshire, the Granite State!
As recently as 1835, geologists believed that huge boulders like Madison Boulder isolated in their surroundings had been washed to their present locations by great floods which are said to have occurred in ancient times. Today, it is believed that these large boulders, or "erratics," were moved various distances during the last ice age.
Most authorities trace Madison Boulder to the Whitton or White ledges 12.5 and 4 miles respectively, to the northwest. However, a few maintain that the boulder so closely resembles one of the four types of rock that form Mount Willard in Crawford Notch, twenty-four miles to the nothwest, that the ice sheet must have brought it from there. Madison Boulder lies on "glacial drift," unsorted sediments left by the retreating ice sheet.