SAN JOSE -- A man in his 50s who is believed to be an observatory employee was killed Tuesday when his Ford Ranger pickup truck went over a guardrail on Mount Hamilton, the California Highway Patrol said.

Emergency crews were alerted to the crash at 12:08 p.m. with reports of an overturned vehicle on Mt. Hamilton Road just south of the Lick Observatory, according to the CHP.

Cal Fire and a Calstar helicopter were summoned, and the driver was pronounced dead the scene.

CHP Officer Peter Van Eckert said it was a solo-vehicle crash, and the deceased is believed to be a state employee for the observatory who was driving up the mountain when the crash occurred.

Van Eckert said the cause of the crash is under investigation and little information was immediately available.

"On that roadway, there's probably not a lot of witnesses," he said. "They will likely have to base a lot of the investigation on evidence at the scene."s

The Santa Clara Medical Examiner's Office had not made a positive identification nor notified the man's next of kin Tuesday evening.