Two boulders about the size of sedans came crashing down the Sardine Canyon mountainside, causing six crashes and shutting down the highway. As heavy rain came down Friday evening, the boulders rolled onto U.S. Highway 89/91 about 9:50 p.m., said Utah Highway Patrl Sgt. Mary Kaye Lucas. The boulders landed between mile markers 4 and 5, just west of Mantua on the Box Elder County side of the canyon. The rock slide led to six accidents, three of which caused minor injuries, Lucas said.