According to this Salt Lake Tribune story, Christiansen was killed after he hit an elk on Highway 6 near Soldier's Summit, veering into oncoming traffic after hitting the animal only to collide with a semi. The two men in the semi were treated for minor injuries and released.
The Tavernacle Website notes that Christiansen had a long history in the music biz. He played in the national finals of the intercollegiate jazz festival in Miami Beach in 1967, the same year he backed up long-time Johnny Carson bandleader Doc Severinson in concert. His rock band Leaves of Grass opened for the likes of The Jefferson Airplane, and after he came to Utah, he spent five years in Chris LeDoux's backing band, Western Underground, and played in the Tempo Timers, backing blues greats at the Dead Goat Saloon.
Most recently, he performed with Chuck Findlay and Eddie Daniels at the Salt Lake jazz festival.