For two years, Rolfe Mandel and his fellow archaeologists thought the dig site they’d been excavating in far western Kansas was special.

Rolfe Mandel, an archaeological geologist at the Kansas Geological Survey, shows off an artifact from a site in Sherman County that dates back 12,200 years, making it the oldest dig site discovered in the Great Plains. The discovery was announced Monday. The Kansas University-based geological survey has been working at the site since 2003 with colleagues from the Denver Museum of Nature.

That feeling has now been confirmed.

Radiocarbon dating just completed on mammoth and prehistoric camel bones at the site confirm it has the earliest evidence of humans in Kansas, and possibly in the Great Plains. The find could change thinking on how early humans came to North America.

“I was very excited,” said Mandel, an archaeological geologist at the Kansas Geological Survey. “We’re excited we can finally talk about it. We were really trying to keep it under wraps until we had all the dates.”

Kansas University archaeologists, along with colleagues at the Denver Museum of Nature and Science, started excavating the site in 2003. Mandel would disclose the location only as being in Sherman County, about a mile from the Colorado border, in order to protect the site for future excavations.

The site, which was first excavated by the Denver museum in 1976, likely was a campsite occupied for a few days or weeks by a small group of nomadic people. It included bones from two mammoths and an Ice Age camel, which appear to have tool marks made by humans. The humans likely were processing the bones to extract marrow, which was a source of food, or to make bone tools.

Carbon-14 dating methods showed that the bones dated to 12,200 years ago. Scientists previously dated the earliest confirmed evidence of humans on the Great Plains at 11,000 to 11,500 years ago, based in part on a mammoth kill site near Greeley, Colo.

“That makes this a very significant find,” Mandel said.

The discovery could change historians’ perspectives on how early humans arrived in North America, said Jack Hofman, KU associate professor of anthropology.

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“If we have evidence of people here more than 12,000 years ago,” Hofman said, “we have to rethink our ideas about human colonization of North America.”

Mandel said the site could give more credibility to the idea that the earliest inhabitants of North America didn’t just cross the Bering Strait from Asia. They may have arrived by boat in South America, then journeyed northward.

In addition to the bones, the archaeologists uncovered stone flakes, tools and pieces of mammoth bone from the Clovis Age, which was 10,900 to 11,000 years ago. Some of the tools came from stone that originated in the Texas panhandle, suggesting the group was highly mobile.

Archaeologists excavate a site in Sherman County, near the Colorado border, which scientists now believe contains the earliest evidence of human existence in the Great Plains. The archaeologists -- including representatives from Kansas University -- have worked on the site the past two summers.

“Clovis materials have been found in Kansas before, but usually on gravel bars along streams,” Mandel said. “This site represents the first central Great Plains discovery of Clovis-period stone tools that are still in place.”

The KU portion of the work is supported by the Odyssey Archaeological Research Fund, an endowed program that aims to find the earliest evidence of humans on the Great Plains.

Mandel said the archaeologists planned to revisit Sherman County starting in June to look for more materials, with hopes of gaining details about how the people who camped at the site fit into the larger picture of early residents of North America.

“This location has the potential for shedding new light on the timing of human entry into the Western Hemisphere,” he said.