The truck's driver - 33-year-old Joseph Paul Czeck - was arrested and booked on two counts of vehicular manslaughter, police said.
Karen Christiansen, 67, and her daughter Jena Christiansen, 32, were traveling behind the truck when it went over a railroad crossing and the huge boulder came off, tumbled and struck the family's vehicle.
Police say the family's Toyota Avalon was headed north on Rich Valley when the landscaping truck came up over a railroad crossing, and the boulder rolled off the truck. The driver of the truck was identified as Joe P. Czeck. Charges are still pending. The photo shows several large boulders in the back of the truck, however, the company's logo was not clear enough to distinguish, Scott said.
Czeck remained in custody Thursday and has declined to give a statement to police, Scott said.
Chief Scott says witnesses heard the rock hit the road and then strike the vehicle. "We had a connection like no other.my heart is broken. the world has lost an angel", Jena's boyfriend Ryan Kilian told KSTP.
Czeck is scheduled to make his first court appearance on Friday.
Officers arrived to the scene Monday afternoon after receiving word of the crash, police said, and found that the auto was hit with a massive rock.
Restaurant manager Jena's boyfriend Ryan Killian said afterwards: 'She is the most awesome person I have ever met.
According to Rosemount Police Chief Mitchell Scott, it appeared the rock had not been properly secured on the truck. Karen, 67, was retired from her job as a training representative at Dakota County Technical College (DCTC) in Rosemount.
'Her father's life, my life, her brothers, she literally was a huge part of Red Lobster.