A boulder the size of a small car slid onto an unoccupied vehicle on U.S. 6 in Clear Creek Canyon in Jefferson County, forcing the road's closure for about seven hours Saturday afternoon, the Colorado Department of Transportation said.The huge rock slid on Highway 6 at Highway 119 and crushed a Toyota that was parked on the side of the road. It belonged to Thomasz Heczko, who had parked it there while he was rock climbing."The gentleman who was driving the car, when he came down he couldn't even see his car. He thought that it had been towed," said CDOT spokeswoman Stacey Stegman.Crews were forced to blow the rock apart using explosives and then drills to get it off the car. They then moved the smaller pieces off the road. No one was injured.Peterson said the cause of the slide had not officially been determined, but he suspected the recent rains, especially Saturdays rains, which would have loosened rocks and soil in the canyon.This is a canyon that is prone to rock fall incidents and with this type of weather, it makes for a very risky situation, Stegman said.She said CDOT is aware of the danger, and spends about $3 million a year on rockslide mitigation.