The bus from the Pasadena-based Light of Life Mission Church hit a sport utility vehicle on Highway 189 near Twin Peaks and veered off the road into a snowy ravine, The (Riverside) Press-Enterprise reported.
The bus driver was pronounced dead at the scene Monday while 10 others were critically injured. Thirteen people sustained minor to moderate injuries, officials said.
The driver of the sport utility vehicle, an off-duty fire battalion chief, and his wife were both injured.
San Bernardino County Fire Capt. Tim Metzger said the accident was one of the worst he's ever seen.
Rescuers had to use ropes and other equipment to haul the injured bus passengers from the ravine to waiting ambulances and helicopters.
The church group was heading home after spending the weekend at the Pinecrest Christian Conference Center in the San Bernardino Mountains.
The California Highway Patrol is investigating the cause of the accident.