The 10 people inside the motor home were believed to be members of a West Richland, Wash., family. Names were not immediately released pending notification of relatives.
The driver, a man believed to be in his 40s, was killed instantly, said Utah Highway Patrol Trooper Anthony Carrubba. The other fatal victims were a 5-month-old boy, a 4-year-old girl, a 6-year-old girl and a 7-year-old boy.
Two women and an 8-year-old boy were flown to area hospitals in critical condition, Carrubba said. Two other children — a 14-year-old boy and another 8-year-old boy — had less serious injuries.
The motor home was traveling northbound on Interstate 15, about 20 miles south of downtown Salt Lake City, on Sunday afternoon. The vehicle went into the median, through a guardrail and then went airborne for about 100 feet before crashing nose first on the highway below.
Salt Lake City saw about 18 inches of snow fall between Christmas Day and into early Sunday, but the interstate was clear and dry at the time of the accident.
"The road conditions were fine," Carrubba said. "There were no skid marks."
Wind at first was thought a possible factor in pushing the motor home from its left lane into the median, but Carrubba discounted that after discovering wind gusts were no more than 19 mph on Sunday.
Contents of the white, 30-foot motor home with blue trim — including a microwave oven, a collapsed sofa and a small refrigerator missing its door — were heaped in a pile on the Interstate 15 median before being heaved into a waiting trash bin.
Interstate traffic in both directions was backed up for miles for about two hours following the accident.