MADISONVILLE - The experts have weighed in, but there are still plenty of theories about the origin of the mysterious crop circles found in a Monroe County wheat field last month.

Local theories range from ancient Cherokee Indian curses to natural electrical or atmospheric disturbances, extraterrestrials and even high school kids with too much time on their hands.

It all started May 14, when Captain Bryan Graves of the Monroe County Sheriff's Office was piloting his small plane in the skies above Madisonville. Graves noticed a strange pattern cut into the fields below. It appeared to be a large circle surrounded by a number of smaller circles.

Investigation on the ground showed that a large field of wheat had been flattened in a circle 170 feet across. Smaller circles radiated out in a pattern that his been described as a "Celtic cross."

The owners of the land had no idea how the patterns were cut into the field and said they had noticed no unusual activity.

The sheriff's office did not formally investigate the incident, but Graves said he walked the field and found nothing that would indicate how the patterns were made or who made them.

"If a complaint had been filed by the land owners we would have approached it from the perspective of vandalism," Graves said.

Hundreds of locals flocked to the site before no-trespassing signs were posted about a week later. Rumors have since circulated about residents seeing lights in the sky and even some who claimed to have seen the formations in dreams months before the circles were discovered.

"I've heard a lot of different stories," said Mark Boring, editor of the "Monroe County Buzz," a local newsletter. "Nobody really knows how or when the formations appeared."

Fortunately, for those with an interest in knowing, there are specialists in this kind of thing, and they have delivered their findings over the past couple of weeks through various organizations and on international Web sites devoted to studying crop circles that pop up worldwide.

"We now have enough scientific evidence to conclude that this formation was not man-made," said Jeff Wilson, the Cincinnati, Ohio-based director of the Independent Crop Circle Research Association.

On Memorial Day weekend, Wilson, 38, led a team of volunteer researchers from around the country to the spot near Madisonville where the circles are, off Rocky Springs Road on land owned by the family of former Tennessee Sen. Estes Kefauver. Wilson's team took more than 1,500 samples from the site.

The nodes of the wheat were microscopically analyzed and found to show unnatural elongation, Wilson said. Furthermore, the stems of the wheat showed evidence of "expulsion cavities" usually not created by natural means but reproducible through the application of heat such as might be produced by microwaves.

The area within the circle also showed higher-than-average levels of radiation and electromagnetic activity. These characteristics have been noted in other plants where crop circles have been found, he added.

"We are using the only peer-reviewed scientific process for analyzing this phenomenon," said Wilson, a network analyst with a master's degree in general science who has been investigating crop circles for almost 20 years.

About 20 to 25 crop circles are reported in the U.S. each year, and the ICCRA is able to investigate about 10 to 15 of them.

Wilson says he considers atmospheric activity, such as tornados and electrical storms, and human activity, including military communications equipment and outright hoaxes.

"In about one in five cases, we can show that they were not man-made," Wilson said." In about one in five cases, we can show that the circles were man-made."

(Original headline: Monroe County thrown for loop by crop circles )