One thing is clear to those who studied a crop circle in Geneseo last summer. It wasn't mechanically produced.

"The indications we do have suggest to us that this was a genuine event," said Nancy Talbott, head of the BLT Research Team, Inc., Cambridge, Mass. "What I mean is, this was not mechanically created. It means something unknown was at work as we have seen in other cases."

What that unknown is may never be known.

When a rural Geneseo farmer discovered part of his soybean field had unusual rings in it last August, he contacted the Henry County Sheriff's Department.

When the BLT Research Team heard about it, the group of scientists sent a soil tester, JoAnne Scarpellini of St. Louis, to investigate.

The retired neurochemist said then that the three circles, about 50 foot in diameter and touching each other, did not appear to be man made.

According to BLT's Web site, www.bltresearch.com, there is no real answer as to why crop circles appear.

Ms. Talbott said there have been obvious hoaxes through the years, but many circles go unexplained. Much of the documented observation is anecdotal, such as animals acting strange or electrical equipment not working.

"Farmers frequently report unusual disturbances among farm animals during nights when crop circles form nearby, particularly reporting that their cattle bellow loudly and/or their dogs bark unabatedly for hours," according to the Web site.

In August 1991, Blue Grass, Iowa, farmer Delmar "Snowball" Meyer found a large crop circle in his cornfield.

"The deputy was out, and he couldn't believe it either," Mr. Meyer said Wednesday. "I had been farming forever. I said to the sheriff, `this is crazy, but I've got a crop circle.' "

Nearly 16 years later, he and his wife, Carol, still have the newspaper clippings from that experience. It never was solved.

Former Davenport attorney and educator Jim Hodges took an interest in the incident. He talked to Mr. Meyer, took pictures, even rented a helicopter to drop inside the crop circle.

"One of the things that does stand out in my mind, when the farmer (Mr. Meyer) was good enough to take me out to the field, his collie dog absolutely refused to walk with us," Mr. Hodges said. "I tried to pick him up and drag him in. He got very ferocious."

Ms. Talbott said scientists were hoping to see something different in the composition of the soil at the Geneseo site. "There have been reports in the past of changes in the nitrogren levels in crop circle soils. We don't see that in this case.

"What we do is take tests in the same fields, but far away from the formation itself. We take quite a few (soil samples) inside the circles, and beginning at the edges, go out in different directions."

Nitrogen levels can increase during lightning strikes, she said. "Farmers know if they live in a lightning-strike area, their soil will be richer in nitrogen."

The Geneseo case is not unlike others across the United States and throughout the world, said Ms. Talbott, who has traveled the world investigating crop circles.

"There are a number of scientists involved in this. But, you've got to remember, just like you and me, they have mortgages to pay and children to raise."

There are anywhere from 15 to 40 crop circles reported in the U.S. each year, she said, adding that crop-circle season starts when things are growing.

"The season has started. Here in the U.S., we start hearing about them in May and it carries through to October. In Red Bluff, Calif., they have found three lovely little circles.

"There was something else reported in Louisiana where 25 circles were randomly placed in a field."

Jim and Christine Dahl, the Geneseo landowners, planted corn this spring in the spot where the soybean crop circles were. Mr. Meyer said they likely won't see a change in growth.

"It's something you can't explain," Mr. Meyer said. "We heard different stories from people afterwards saying there were lights in the sky when this happened, that their wells got real cloudy days after that.

"We had a call quite a while later from someone in Wisconsin saying him and his son were driving from Wisconsin someplace and all of a sudden, they were in a motel in Bettendorf.

"And they didn't know how they got there. So much stuff happened."