Ten people sustained serious injuries and 13 had minor to moderate injuries, according to the California Highway Patrol. Doctors said two patients remain in critical condition - a teenager who went into surgery and a woman in her 20s.
The CHP said it would release the name of the deceased once the next of kin had been notified.
Officials called it a mass casualty situation, and victims were taken to every available county hospital.
The bus collided head-on with an off-duty San Bernardino County Fire battalion chief and his wife in his own vehicle, a Nissan Murano, on SR-189 near Lake Gregory Drive just before noon. He and his wife were at home recovering from their injuries Monday evening.
The bus was carrying 22 people including middle and high school-aged kids, members of a Korean church called Light of Love Mission Church in Pasadena. The bus had departed from the Pinecrest Christian Conference Center in Twin Peaks.
The collision sent the bus about 50 feet down a snowy embankment and crashed into a tree, according to the Callifornia Highway Patrol.
One person on the bus was pronounced dead on scene, while others were taken to area hospitals.
According to a Pastor Joe Lee at Light of Love Church, the group of students was on a retreat to pray and meditate and were on their way back.
"I see blood just basically everywhere you look, and I didn't see one person that didn't have blood on them," said Crestline resident Vernal Shultz. "I come up and there's this one little girl, I'm assuming 9 years old, and she's just sitting there and she's hurting -- it just got me. She's sitting there apologizing for being a problem, for being trouble. I'm saying, 'You're no trouble, come on, it's all going to be good.'"
"Very chaotic, as you can probably imagine," said California Highway Patrol Officer Mario Lopez. "A lot of agencies came together to try and rescue the individuals involved in this collision."
Several rescue crews, ambulances and helicopters were sent. The roadway was shut down during the rescue effort, but it has since reopened.
There were no indications alcohol contributed to the crash. The weather did not appear to be a factor either.