08/26/2026
America's Stonehenge is located in the Granite State, so where's all the granite? Swap your archaeology hat for a geologist's helmet and get ready to dive beneath the surface of New Hampshire's ancient history!
The bedrock in southeastern New Hampshire is composed mostly of metamorphic rock that was created more than 400 million years ago when tectonic activity changed the ancient coastline of North America. If you remember high school Earth science, you'll know that granite is an igneous rock, not metamorphic, because it is formed by cooling magma and volcanic activity.
While the metamorphic bedrock of coastal New England was being formed, there were also volcanic forces at work. Magma was pushed up into the Earth's crust, where it was trapped below the surface rather than erupting as a true volcano. These pockets of magma slowly cooled, creating patches of igneous rock called plutons.
America's Stonehenge is located on the southern edge of one such pluton, named the Island Pond Pluton for the body of water that covers most of the igneous deposit. This pluton contains classic New Hampshire pink granite as well as diorite and quartz crystals. After millions of years of erosion and glacial activity, the Island Pond Pluton has been exposed as surface rock, especially in the hilly terrain of this area. When the ancient builders encountered the unique geology here, they incorporated these rocks into the megalithic structures we know today as America's Stonehenge.
While the human history of America's Stonehenge can be traced back 4,000 years, a visit to this scenic historic site in Salem, New Hampshire will actually show you hundreds of millions of years of New England's past!
