As heavy machinery scraped the site of a highway project near Lake Minnetonka, something unusual turned up in the dirt: quarter-sized fragments of bone. That was enough to stop the machines, because the on-site archaeologist knew that Hennepin County was digging the site of Indian burial mounds first mapped in 1883.

State Archaeologist Scott Anfinson had signed off on the project, after several surveys convinced him that any artifacts or remains were probably long destroyed.

But on that day last October, Anfinson got the bad news. For the first time in his 10 years in the job, he had given the green light to a project through a known archaeological site, only to find out that it was still an ancient tomb.

The discovery halted work on a planned roundabout that would eliminate a dangerous 90-degree curve on Hennepin County Road 101. Last week, Hennepin County engineers met with tribal and archaeological representatives to start mapping the way forward.

"It's real upsetting to tribal people," said Jim Jones, cultural resources director of the Minnesota Indian Affairs Council. "It shouldn't have happened. Now we have to fix it."

Jones said the road design will have to change in order to preserve what's left of the mounds. His voice holds significant sway — state law gives the council the authority to protect American Indian burial sites.

The Legislature granted that authority in 1976 to stop the widespread bulldozing of Indian mounds, which hadn't been afforded the same protection as white cemeteries. Bones still turn up in construction projects all the time, but those are typically grave sites not on any map.

Minnesota is home to an estimated 12,000 known mounds, the final resting places built by Indians from about 500 B.C. through 1500 A.D., Anfinson said.

When T.H. Lewis first surveyed an area on the eastern edge of Lake Minnetonka, he mapped 52 mounds that came to be known as the Shaver Mounds. A 1911 book described them as "a remarkable series, both for their number and uniformity of size" and noted that one was 270 feet long.

Years of development, including a railroad cut for the Deephaven streetcar line, obliterated most of what's now known as site 21HE27. "You couldn't see a single one of the burial mounds on the surface any more," Anfinson said.

Starting in 2008, consultants dug into the site to see whether any trace of the mounds remained intact. In 2010 the Indian Affairs Council dispatched its own consultant, who said that based on soil cores and Lewis' notes the mound remnants still existed in the project's proposed footprint. Anfinson's office disagreed with that conclusion, saying the council's consultant had his map wrong. Hennepin County hired a third consultant, who extracted 45 soil cores and found "no evidence for any surviving mound fill, burial pits, bones, or artifacts," according to a 2011 report by the state archaeologist.

Still, because of the site's long history, Anfinson said he required an archaeologist to be on-site when grading began last fall. Jones got the call on a Sunday at his home in Cass Lake. The next day, Oct. 13, he went to the site with Anfinson and a representative of the Shakopee Mdewakanton Sioux Community.

"We cleaned off the area where the original find had been," Anfinson said. They could not say for certain the initial bone fragments were human. "Finally we found a tooth. … At that point, I looked at Jim. I said it was a human tooth."Because it was an Indian burial ground at one point, Anfinson determined the remains were "ethnically Indian" and thereby the responsibility of the council.

The incident was especially disturbing to Jones, because the council's consultant had already warned against construction. His frustration was compounded by the discovery that same day of the bones of 19th-century American Indians by someone building a lakeside home near Pine City.

"It is our hope that these unfortunate and preventable incidents will help inform and educate those involved and help prevent further such incidents from happening in the future," the council wrote in its annual report, submitted in December.

Anfinson said the county did its due diligence, commissioning two studies rather than the usual one. "This is on everyone's mind," he said. "No one's happy about this."

Last week, a thin layer of snow covered the disturbed grave. Here and there were planted little plastic flags, and taller wooden stakes bore the words, "Lewis Survey," noting the work of a man who had passed this spot 132 years earlier.

Contact James Eli Shiffer at james.shiffer@startribune.com or 612-673-4116. Read his blog at startribune.com/fulldisclosure.