LOVELL - Looters and collectors got there first in almost every case, but enough evidence may remain in the hundreds of tepee rings that cover Bighorn Canyon National Recreation Area to fill information gaps 10,000 years wide.

"The nice thing about tepee rings is that most people don't pick up the rocks and take them away," said Laura Scheiber, an archaeologist from Indiana University conducting her fourth field school on the park's Bad Pass Trail.

She was standing on the edge of a park road recently amid circles of red, blue and orange survey flags flapping in a 20 mph wind. The flags mark some of the 35 tepee rings her students have mapped this year. They may get to another 20 farther upslope before the survey ends later this month. Across the road, 60 more have been identified.

All of the rings are pre-horse and prehistoric. Once Euro-Americans introduced tools like axes, historic tribes used wooden pegs instead of stones to keep skirts of their hide tepees anchored to the ground, Scheiber said.

Bad Pass Trail has been traversed probably since the earliest human habitation of the continent. It brought people from the Big Horn Basin onto the plains of Montana, perhaps in seasonal rounds that took them to abundant bison herds beyond the mountains.

"It's been used for 10,000 to 12,000 years," said Chris Finley, National Park Service archaeologist at Bighorn Canyon.

Last season, on a bluff near this year's survey site, the field school found a projectile point that dated to 8,500 years ago.

But most cultural material - arrowheads, spear points and tools that offer clues to era and everyday life - have disappeared in the 100 years or so since the frontier was settled, Scheiber said.

But in hearths, where bones, seeds and charcoal can be identified and dated, they may find some answers.

There is certainly no shortage of questions.

How did people across 10 millennia make their living in this high, dry country between the Pryor and Big Horn mountains of northern Wyoming and southern Montana? Did they travel in small family groups and revisit the same sites season after season? Were concentrations of these stone circles evidence of a large seasonal gathering, or do they represent smaller encampments over long periods of time? Did they stay a few days or dig in for the spring or fall?

Who these people were, we may never know. But researchers from Indiana University in Bloomington, Northwest College in Powell, and Little Bighorn College at Crow Agency, Mont., believe that some 300- to 400-year-old rings can be attributed to an early Crow presence in the canyon.

A field school that brought 19 undergraduate students and two graduate students from around the world to study the tepee rings on the southern end of the recreation area have been mapping every single rock on their site on the north end of Mustang Flats down to a fraction of a centimeter.

Under the watchful eyes of their professors, Scheiber and Judson Finley of Northwest College, they note, mark, map and learn how a field archaeologist works. Ethnographer Kelly Branam of St. Cloud State University in Minnesota helps them interpret the social setting of the campsites and relate it to traditions of modern native peoples. Before they headed to the canyon, the students camped out on the Crow Reservation to learn the stories and traditions of that ancient culture and how it has integrated into modern life.

Throughout the 20-day field school - 10-day sessions on either side of a four-day break - students and teachers camp at the historic Ewing-Snell Ranch, where the National Park Service has set up a science and learning center.

Outdoor life with a fast-running creek for bathing and a tent for shelter bring the students closer to what native peoples had to deal with every day, Scheiber said.

"They learn how to manage food for 25 people with different needs," she said. "How to live together when you can't go anywhere."

Branam also pondered the advantages of a hide-covered shelter.

"Tepees must have been a lot drier than my little tent," she said.

Sun breaks were rare in the first session of the field school. Rain has been almost constant.

Chris Finley chooses the site for the field school each year, and the Park Service helps with some of the costs.

"Most sites have already been looted," Finley said. "I look for sites with low-energy slope-wash deposits that have the potential to preserve the living surface - spots that would have been looted if they'd been exposed."

Using remote sensing technology, they have been able to identify hearths in some of the rings and will excavate the most promising for materials that can be carbon-dated. Finley says the Park Service has paid to have four samples carbon-dated each summer.

Last year's results produced a wide range of dates. Two rings, which may have been associated, were in use about 500 years ago. A sample from a larger tepee dated to 2,500 years ago.

"There is this idea that with the horse and their ability to carry heavier things than humans and dogs, that tepees got bigger," Scheiber said. "That may be true, but so far we haven't seen complete correlation between time and size."

The tepee ring oldest in date was largest in size, she said. The ring from 2,500 years ago was 6.5 meters in diameter - about 21 feet. The later rings were 4.5 and 5 meters in diameter.

Their finds also challenge assumptions that tepees always opened to the east, Scheiber said. Some opened to other directions, possibly in line with prevailing winds or to maximize sunlight.

Later stone circles have characteristics that often are found in Crow tepees.

"The Crow put up their tepees in a very different way from other tribes," she said. "They use four poles instead of three. With a four-pole foundation, tepees are more circular. Three-pole tepees tend to be more egg-shaped. A lot of these are very circular shaped."

Stone circles aren't an exact measurement of the circumference of a tepee. When it was time to move, the rocks would have been pushed out and off the hides so the tepee could be wrapped for transport.

Field school teams didn't find any rings with interior circles that would indicate that tepee liners had been used during cold winter weather, Scheiber said. And that may mean that the area was used from spring through fall.

"I have the sense that people were coming up and down the corridor with extended families and probably not staying very long," she said. "I think they were moving along fairly rapidly."

One thing Scheiber hasn't found is pottery.

"I always think I'm going to find ceramics," she said. "I've always got my pottery eye on. I've not found a single piece, but I know it's out there."