Authorities are investigating an incident of vandalism that caused tens of thousands of dollars worth of damage over the weekend. The crime occurred at Hoffman Concrete in Mankato. When the owner arrived at the business Monday morning he discovered someone had caused as much damage as possible with his equipment. A forklift was used to try and ram one dump truck into another. When the vandals were unsuccessful in that attempt, they apparently used the forklift to break through a door. A Ford truck was then used to knock over several oil drums. The total amount of damage is being estimated at around at least $30,000.