BILLINGS, Mont. (AP) -- A government archaelogist believes ancient fire pits and pottery recently unearthed in south-central Montana are the works of an Indian culture that disappeared hundreds of years ago from its home range in modern-day Colorado and Utah.

Glade Hadden, a Bureau of Reclamation archaeologist, said evidence found at the site near Bridger strongly suggests the area was inhabited by Fremont people, an Indian culture known for its masonry work and fine pottery.

"There is no doubt in my mind," Hadden said.

His could be a controversial conclusion, but it could also provide a clue to determining what happened to the Fremont people, who are believed to have disappeared from their home range in the 14th century.

The Fremont people lived in what is now Utah and Colorado, mostly from about 300 A.D. to 1200 A.D.

"Then they disappeared," Hadden said. "I mean they flat disappeared. No one knows what happened to them."

Last month, while on an excavation south of Bridger, Hadden said he saw a piece of ancient earthenware that he immediately recognized.

"I knew right away that it was Fremont pottery," he said. "I grew up with Fremont pottery. I know what it looks like."

Working with students from Montana State University-Billings, Hadden also unearthed an intricate fire pit that further convinced him of the significance of the find.

The pit, about 20 inches deep and 2 feet wide, was expertly lined with a thin layer of sandstone slabs. The joints were plastered with mud and worked to a smooth surface, all identical to the work of Fremont people, said Hadden, whose wife was also involved in the excavation.

"We've dug a lot of fire pits over the years, but I've never seen anything like the amount of work that was put into this one," said Johanna Hadden, an assistant professor of education at MSU-Billings.

Hadden has yet to submit samples of the items found for tests that could determine their age. But he said the site appears to have been in use sometime between 1400 and 1600.

If his theory is correct that the site was inhabited by Fremont people, the question becomes: How and why did they end up moving so far north from their historic range?

Questions remain about whether the Fremont people were assimilated, annihilated or forced north by intruding people, Hadden said.

Hadden suspects a combination of environmental factors and aggressive newcomers may have resulted in a move north.

"We want to find out what kind of people were here and what were they doing," he said.

In Utah this spring, researchers announced they had found a well-preserved Fremont site on a former ranch. The Range Creek site, protected from intruders for 50 years by the rancher who owned it, reportedly contains large numbers of rock art sites, remote granaries in the rock wall and pit houses.