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SPRAGUE — The farmer and her son were scouring their fields before planting season, picking up rocks to keep them from damaging their equipment.

Konnie and Marcus Robertson spotted a piece of pink sticking out of the ground about the size of a football.

They started digging. And digging.

It was too big for a shovel, too big for their skid-loader, too big for the tractor and bucket. They finally tapped a pair of Caterpillar bulldozers to pluck it out of their field and push it a quarter-mile to their yard along West Stagecoach Road.

They planted it in a landscaped berm, next to some of their smaller discoveries. And 12 years later, Konnie Robertson emailed the newspaper.

Because earlier this month, on a slow news day, we wrote about a big boulder in a backyard along West A Street — a 44,000-pound lawn ornament the size of a shed — and we challenged you:

If you have one bigger, we’ll write about you, too.

We heard about Konnie Robertson’s rock from her — and from others who had driven by.

“We’ve got a bunch of other rocks on our property we dug up and moved around that are pretty impressive on their own,” Robertson said. But this one dwarfed them all.

Her husband, Russ, had taken its dimensions and headed to Morrill Hall, where rock experts estimated it weighed 60 tons.

We heard about smaller rocks that we’re not writing about.

We also heard about a rock in Wahoo that’s big, though not bigger than the boulders on West A or West Stagecoach.

But the Wahoo one has history. For years, it was one of the Twin Rocks, a pair of guideposts along an important pioneer route, the Ox-Bow Trail, which carried wagons westward from Nebraska City to Fort Kearney, said Erin Hauser, curator of the Saunders County Historical Society museum.

The trail — also known as the California Trail, Military Road and Mormon Road — was used during the heart of the 1800s, and the boulders near Swedeburg in Saunders County greeted scores of miners, freighters, soldiers and settlers.

Years later, one of the twins ended up at a Gretna landscaping company. “And then it was rescued and donated to us,” Hauser said.

In the early 1990s, when the museum built an addition, the survivor was moved to its front yard. It was so heavy it broke the forklift moving it, she said, delaying the end of its trip.

Interesting stories about where these boulders finally ended up. But Matt Joeckel has a story, too, about how they landed in Nebraska in the first place, because they’re not from these parts.

First, the state geologist gives a vocabulary lesson: These boulders are called erratics.

“Not someone like me, who is half-crazy,” said Joeckel, a professor in the Conservation and Survey Division of UNL’s School of Natural Resources. “An erratic boulder is a rock that is clearly and absolutely out of place.”

The genesis of the rock mass that spanned these boulders — Sioux quartzite, the hardest rock in Nebraska — began more than 1.5 billion years ago in what is roughly the Sioux Falls, South Dakota, area.

Before the middle 1800s, geologists were stumped by erratics.

“The only explanation that people could come up with at the time was they were deposited by the Biblical flood,” Joeckel said.

But by the 1860s, geologists had accepted erratics as evidence that ice sheets had advanced, retreated and advanced again over the course of 2.6 million years — the Pleistocene, which ended 11,700 years ago.

Around here, the Laurentide Ice Sheet originated in what is now Canada and reached into eastern Nebraska at least a half-dozen times, plucking and plowing weathered and weakened bedrock at first, then stronger formations.

Like the Sioux Quartzite Ridge. When dinosaurs still roamed, 90 million years ago during the Cretaceous period, part of the ridge was an island, rising out of the big interior sea that covered what is now the Midwest.

But the ice sheet pushed pieces of the ridge south, leaving them on what would become Konnie Robertson’s corn field, and on a pioneer trail stop a few miles from Swedeburg, and on farms between here and Sioux Falls.

“It was ripped up by the glaciers and carried down here,” Joeckel said. “Anyway you look at it, it was an interesting story.”

A discovery the size of Robertson’s is rare, he said. Not many of the big boulders survived the black powder and dynamite used by early farmers trying to clear their fields.

That’s what happened along the Ox-Bow Trail: An early landowner blasted one of the Twin Rocks to pieces before neighbors explained their significance and stopped him from destroying the other.

Joeckel likes to talk about rocks. How they formed, how they moved, how they shaped where we live. Humans are in touch with the world around them, but too few are aware of what played out beneath their feet.

“People need to be better aware of their geologic setting,” he said. “There is a vastly fascinating story behind those boulders.”

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Reach the writer at 402-473-7254 or psalter@journalstar.com.

On Twitter @LJSPeterSalter.

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Reporter

Peter Salter is a reporter.

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