Bedrock Geologic Map of New Hampshire

_{Courtesy New Hampshire Department of Environmental Services}

New Hampshire was once like the Alps of Europe—thick sediment sequences, volcanic deposits, bodies of granitic rocks pushed slowly up from below. The state lay on the edge of the continent as a new ocean basin opened and then closed nearby. That ocean was not today's Atlantic but an ancestor named Iapetus, and as it closed the volcanic and sedimentary rocks of New Hampshire were thrusted and kneaded and heated until they became schist, gneiss, phyllite, and quartzite. The heat came from intrusions of granite and its cousin diorite.

All this history took place in the Paleozoic Era from 500 to 250 million years ago, which accounts for the traditional dense, saturated colors used on the map. The green, blue, and purplish areas are the metamorphic rocks, and the warm colors are the granites. The general fabric of the state runs parallel to the rest of the mountain ranges of the eastern United States. The yellow blobs are later intrusions related to the opening of the Atlantic, mostly during the Triassic, around 200 million years ago.

From then until nearly the present, the history of the state was one of erosion. The Pleistocene Ice Ages brought deep glaciers to the whole state. A surface geologic map, showing the glacial deposits and landforms, would look very different from this one.

I have two apologies. First, I left off the tiny Isles of Shoals, which sit offshore past the lower right corner of the state. They look like dirt specks, and they're too small to show any color. Second, I apologize to my old professor, the map's first author, for the mistakes I've surely made interpreting this map.

See this map at two larger sizes, 800x1050 pixels (230 KB) and 1200x1600 pixels (340 KB). Or you could get your own copy from the state Department of Environmental Services for a mere 50 cents.

More about New Hampshire Geology

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