Long before Europeans explored North American soil, a population of people flourished in the Mesa Verde area of southwestern Colorado, erecting elaborate stone structures, farming the fields and making pottery.

The Ancestral Puebloans are believed to have lived in this pocket of the southwest for more than 700 years, with a population that may have reached several thousand.

But then, somewhere around the year 1280, the population suddenly crashed.

In the world of archaeology, that much is agreed upon. What isn't so clear is how, why or what happened to the people who once inhabited Mesa Verde.

Dr. Scott Ortman, an archaeologist who lives and works in Cortez, has been pondering the issue for 15 years. And after devoting his doctoral dissertation to the subject, he has come up with a compelling theory on what happened to the people of Mesa Verde.

Ortman will be discussing it in a slideshow presentation Thursday night at the Telluride Historical Museum. The Telluride Unearthed lecture, "Archaeology, Oral Tradition and the Mesa Verde Migration," is at 6 p.m. It is $4 for members of the museum, and $6 for non-members.

Ortman is the director of research and education at the Crow Canyon Archaeological Center in Cortez, and has been working there in one capacity or another since 1993.

After doing archaeological work in the Four Corners for years, he decided to tackle the Mesa Verde question in his doctoral dissertation for Arizona State University. In the end, he laid out the case for a rapid depopulation of the Mesa Verde Area by the Tewa-speaking people, who migrated en masse to upper Rio Grande basin.

Ortman's theory is that this population reinvented itself when it moved in a sort of social revolution, an upheaval that resulted in its population changing its architecture and style of pottery.

"I tried to make a concrete claim about how they are related," Ortman said.

Ortman mostly used existing data, culling from the vast body of archaeological evidence out there, and melded disciplines such as computer science, ecology, geology, biomolecular science and linguistics in his project.

Armed with these tools, he studied the genes, language and culture of the Tewa people, who have inhabited and area of the Upper Rio Grande for centuries. What he found led him to believe that these people have roots in Mesa Verde.

The connection isn't obvious on the surface, because the style of pottery and building tied to the Tewa varies from that of the people of Mesa Verde, but Ortman found language connections between the places. In addition, he found population patterns that indicate the population of the upper Rio Grande region grew rapidly following the decline of the population of Mesa Verde.

His theory is that a cultural revolt left to an exodus, and the people consciously changed their culture after they left - much as the English revolution resulted in a whole new identity of a population.

"I've done a number of other studies that led me to conclude that the disjunction you see was because of social process," he said. "I think it was some kind of revolution."

This event will be hosted by the museum in conjunction with the Pinhead Institute.

Participants can follow up this presentation with a Crow Canyon Field Trip on June 16. Join the Telluride Historical Museum for an informative bus trip to Crow Canyon followed by a scholar guided tour of Crow Canyon and an excavation site. See www.telluridemuseum.org for more info.