The crash happened at about 11:40 a.m. on Alhambra Valley Road near Deodara Way, California Highway Patrol Officer Tom Maguire said.
Turkington had been driving east on Alhambra Valley Road in a Ford Econoline van when he suddenly veered off the road, crashed through a fence and hit a tree.
A passerby stopped and rendered aid until paramedics arrived, but Turkington died at the scene, Maguire said.
Investigators believe the crash may have been caused by a medical condition. Drugs and alcohol are not suspected.
There were no passengers in the van and no other vehicles were involved in the crash, Maguire said.