It was not immediately clear who was buried in the graves and how long the bodies had been there.
The grisly discovery came hours after suspected drug hitmen killed Hermila Garcia, the 36-year-old police chief of the town of Meoqui in Chihuahua state -- a rare deadly attack on a female Mexican law enforcement official -- the Chihuahua state attorney general's office said.
Garcia was killed early Monday as she drove her vehicle through the town, in what could be a warning to a string of other women who have recently taken on senior police jobs in Chihuahua. The state is home to Ciudad Juarez, Mexico's most violent drug war city.
The drug violence that has killed more than 31,000 people across the country since December 2006 is tarnishing the country's international image and worrying Washington and some investors.