YUMA, Ariz. – The Mexican consulate in this city launched a campaign in recent days to warn their countrymen of the dangers of trying to cross the desert into the United States at this time of year.

That warning apparently came too late for at least eight people whose skeletal remains were found Saturday.

Authorities in the Mexican state of Sonora reported Sunday the discovery of the remains in several sites around the border town of Sonoyta believed to be undocumented immigrants who died in the scorching heat.

The remains, which did not show signs of violence, were found on the border between Sonora and Arizona, in a radius of several miles, Sonora state police said in a statement.

"It is assumed that they died of heat exposure," the statement said.

It said that a group of men from the Sonora city of Caborca traveling on horses through several ranches discovered the remains.

It's estimated that the remains were from three months to one year old.

Authorities reported that the migrants died less than half a mile from the border and that some remains were found under trees.

According to the statement, members of Grupo Beta, Mexico's border surveillance agency, were able to identify four of the victims through belongings found on the remains. All of them were Mexican citizens.

Despite a crackdown by U.S. border authorities, and the recession, thousands of people try to cross the border illegally each year through the Sonora desert. They encounter severe dangers, such as the weather extremes of heat and cold, organized criminals and corrupt Mexican officials.

The Mexican Consulate in Yuma issued its warning on July 6 after U.S. Border Patrol agents found the bodies of five people who apparently perished in the punishing desert heat the previous week.