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Receding glaciers left these rocks behind in what is now New York City's Central Park. Inspired by the "childish playfulness … of Nature," Frederick Law Olmsted, the park's co-designer, often did nature one better and arranged the boulders, known as erratics, into what he considered poetic tableaux.
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The erratic in the foreground tumbled from a mountainside onto Mendenhall Glacier in Juneau, Alaska. Sliding downhill, sometimes two feet a day, the ice will eventually crumble, dumping its rider into Mendenhall Lake.
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"Leaverites"—leave 'er right there—is another nickname for erratics too big to move, like the one by a parking lot in Mystic, Connecticut. But developers haven't always left 'em right there.
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This erratic stands where it was deposited by a glacier; the town of Glen Rock, New Jersey, grew up around it, and Doremus Avenue makes its way on either side. Take a right at the stop sign and you're on Rock Road, which leads to the center of town. Glen Rock's rock has several names: the Rock, the Great Rock, and the Big Rock among them.
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Glen Rock, New Jersey, is named for its 570-ton erratic. Scientists believe a glacier brought it from about 20 miles north. The Lenape Indians, who inhabited the area, had another idea. Their name for such a rock was pamachapuka—stone from the sky.
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Boulders perch randomly at Olmsted Point in Yosemite National Park. A glacier sculpted the 92-million-year-old bedrock here and left the boulders, plucked from a nearby mountain, when it retreated. The rocks, along with grooves in the bedrock, show the path of the glacier.
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Boulders plucked from a nearby mountain rest on the polished expanse of Yosemite's Olmsted Point, elevation 8,400 feet. The glacier that carried them flowed into adjacent Tenaya Canyon and grew to thousands of feet thick.
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Looking as if it fell from the sky, a 40-ton erratic stands on the Colville Indian Reservation in Washington State. Such boulders are sometimes called rubbing stones because bison scratched up against them.
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Yeager Rock (at right), in north central Washington State, helped geologists map how far south the ice sheet pushed—and provided a surface where local graduates could paint important dates.
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Brenda Diaz and Jessica Ruiz take a break near the rock during a road trip. Indians used to mark boulders with carvings. Today's artists, some of whom have immortalized the years of their high school graduations here, prefer paint.
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When the O'Boyles moved to Stonington, Connecticut, an area once covered by glaciers, they thought the rocks in their yard, like erratics nearby, had been delivered by ice. A visit from the Connecticut Geological Survey proved them mistaken, but the O'Boyles remain die-hard members of the big-rock fan club, taking meticulous care of the boulders in their lives.
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Two images stitched together show boulders on Pyramid Mountain in Morris County, New Jersey. On the left, an erratic named Tripod Rock balances its 160 tons on three smaller glacial erratics. Embedded in ice and glacial debris at first, the boulder and its unlikely supporters are what remain after 19,000 years of erosion. The two boulders at the far right are called solstice stones, because the setting sun on the summer solstice lines up between them.
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A melting iceberg, calved from the snout of Alaska's Mendenhall Glacier, carries a passenger just a bit farther. This rock tumbled onto the glacier back in the mountains and rode the escalator down to Mendenhall Lake.
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