A 52-year-old Modesto man was killed in a solo vehicle collision Monday afternoon when his truck struck a boulder in Denair.

The man was identified by the California Highway Patrol as Gary Arnebeck, Jr.

The accident was reported at 1:50 p.m. Monday at the intersection of Tuolumne Road and Gratton Road.

Arnebeck was driving a 1999 Ford ranger eastbound on E. Tuolumne Road. He was approaching the intersection with Gratton Road, which forms a T-intersection, when for an unknown reason he suddenly began accelerating, according to the witness statements.

The Ford was traveling at a high rate of speed as it went through the intersection and collided with a large decorative landscaping boulder, the CHP reported.

The impact caused the vehicle to come to a sudden and complete stop. The collision caused major damage to the front end of the Ford, trapping Arnebeck inside. Emergency responders tried to free Arnebeck from the wreckage, but he was ultimately pronounced deceased at the scene.

Investigators are looking into the possibility Arnebeck suffered some type of medical emergency preceding the crash. Alcohol was not considered to be a factor in the collision. Arnebeck was wearing his seat belt at the time and his air bags were deployed, the CHP reported.