Giant Rocks

Where did these big boulders come from?

Many thousands of years ago during the last ice age, these boulders would have been embedded in the Laurentide Ice Sheet, which covered much of the Northern Hemisphere. To picture the height of this immense glacier (over 5000 feet), imagine two Mt. Kearsarges stacked on top of each other. About 13,000 years ago as the planet warmed and the southern edge of the glacier retreated northward, these big boulders – called glacial erratics – along with numerous smaller rocks, known as glacial till, were deposited here as the ice melted.

The glacier’s retreat was a slow process, taking at least 1,000 years for the edge of the ice sheet to move from New Hampshire’s southern border with Massachusetts to its northern border with Quebec. (Of course, there were no states or provinces at that time.) Only after a few more thousand years did the kinds of forests we see today begin to exist here.


Tom Wessels, Reading the Forested Landscape: A Natural History of New England

Whit Bronaugh, “North American Forests in the Age of Nature,” American Forests,

David Ullman, University of Wisconsin, Department of Geoscience, “The retreat chronology of the Laurentide Ice Sheet during the last 10,000 years and implications for deglacial sea-level rise”