When the state Department of Transportation began construction on a bridge over the Farmington River, archaeologists suspected there could be historic sites hidden under the soil.

In late 2018, once excavation was underway, crews discovered evidence of what scientists have called southern New England’s earliest inhabitants.

The site, located near Old Farms Road, is estimated to be about 12,500 years old, dating back to a time known as the Paleoindian Period. It has been named in honor of Brian D. Jones, the state archaeologist, who died in July.

The Paleoindian site is the crowning discovery after years of archaeological digs in that part of Avon, according to Catherine Labadia, a staff archaeologist with the State Historic Preservation Office.

Labadia said previous excavations have uncovered younger sites. But the DOT project allowed for a deeper dig — and more significant finds.

“This is the once-in-a-lifetime opportunity to look at this age of a site in Connecticut,” Labadia said. “This site has the potential to make us understand the first peopling of Connecticut in a way we haven’t been able to.”

The DOT hired a Storrs-based firm, Archaeological & Historical Services Inc., to conduct the dig itself. The principal investigator on the dig, Senior Archaeologist David Leslie, said excavation turned up about 15,000 artifacts and 27 features.

Artifacts in this case were mostly tools — and the archaeologists count each small fragment as an artifact.

Features, Leslie said, are more rare.

In general, features are remnants of human activity, including holes and walls — what Leslie described as “traces of behavior” that have been recorded in the earth. At the Avon site, Leslie said, archaeologists found an open fire pit, or hearth, and a number of posts from temporary houses.

Only a handful of Paleoindian features have ever been discovered in this part of the country, Leslie said, and the Avon site revealed more than two dozen.

The site shows evidence of the earliest known population in Connecticut, she said. “Right now, this is the oldest. And people have been looking for Paleoindian sites for quite some time.”

The Avon site was discovered as DOT prepped to reconstruct the Farmington River bridge at Old Farms Road, near Route 10. The project cost a total of about $14.7 million, the Courant previously reported.

In this project and in any others, DOT is subject to the National Historic Preservation Act, which requires agencies to look into potential historic landmarks before building on or disturbing a site.

Because there often isn’t enough funding for independent archaeology research, many discoveries come about after a state or federal agency starts a construction project, according to both Labadia and DOT staff archaeologist Scott Speal.

“Far and away most of the archaeological resources that get investigated happened through ... agencies doing their work, going about their business and spending money,” Speal said.

In the case of the Avon site, the DOT project required deep excavation for the construction of bridge abutments. Labadia said that such a deep dive — the artifacts and features were lodged about 6 feet under the surface — would likely have been cost-prohibitive to archaeologists working on their own.

“It is these federal laws and the requirements that make people stop, look and listen,” Labadia said. “It’s those laws that really have resulted in the largest identification of archaeological sites.”

Leslie, the site’s principal investigator, said that the DOT agreed to “100 percent data recovery” of the Avon site, meaning that the plot of land was fully excavated and each patch of dirt was sifted through for artifacts.

“They afforded us time and money to excavate the entire site,” Leslie said. “We preserved it through excavation.”

The Avon site and all of its artifacts may have been left undiscovered if not for the work of Brian Jones, an archaeologist who worked at Archaeological & Historical Services and later became the state archaeologist.

Jones, who died over the summer after a battle with cancer, had a “knack” for finding Paleoindian sites, Leslie said.

DOT first hired the Storrs-based archaeology firm in 2012 to 2014, Leslie said. The DOT tasked the firm with conducting an initial site survey of the Avon site, which Jones led.

But that survey didn’t turn up anything of note.

Nevertheless, Jones wrote in the survey report that he believed there may be something lurking deeper below the surface, in part because of the site’s proximity to the river.

The DOT project then was stalled for several years, but the need to dig deeper was included in the project’s memorandum of agreement, Leslie said.

In 2018, when Jones was the state archaeologist, his former firm was once again contracted for work at the site. This time, the crews dug about 5 feet down, Leslie said. Within a week or two, with artifacts and features already popping up, they realized they’d found a Paleoindian site.

“Many other archaeologists, I think, have missed sites that are deeply buried because we’re used to only investigating the top few feet,” Leslie said. But “Brian had a feeling that there could be the potential for archaeology here.”

Even after Jones was diagnosed with cancer, he would visit the site regularly, offering his advice and expertise to the archaeological crews.

“Brian was battling cancer throughout the past year ... and yet he still found time almost every week to be on site with us,” Leslie said.

Labadia, of the State Historic Preservation Office, said the site discovery felt like a final ode to Jones’ years of dedicated work.

“It was almost like a gift that was given to him,” Labadia said.

To honor Jones and his work, the Avon site has been dubbed the Dr. Brian D. Jones Paleoindian Site.