A Calgary mother in a Subaru died when a large rock thrown by a passing truck hit her in the head on the Kootenay River Bridge.

The mother of two and her family were driving across the Kootenay River Bridge on Highway 93/95 in southeastern B.C. on Friday when the rock,  smashed through her car's window and hit her in the head, killing her instantly.

Police believe the rock, which they say measured 30 centimetres by 13 centimenters in diameter, had been wedged between the dual wheels of the truck's trailer.