SAN RAFAEL (CBS SF) — A motorcyclist was killed Thursday afternoon when he collided with a dump truck in unincorporated Marin County near San Rafael, a California Highway Patrol officer said.

Three motorcyclists were traveling west on Lucas Valley Road west of Westgate Drive through a series of turns around 12:15 p.m. when the front two riders pulled away from the rear rider, CHP Officer Andrew Barclay said.

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The rear rider drifted into the eastbound lane of Lucas Valley Road on a curve into the path of a 2013 International Harvester dump truck registered to the Marin County Department of Public Works, Barclay said.

The truck driver, whose name was not available, hit the brakes but the motorcycle struck the front of the truck, Barclay said.

The male motorcycle rider died at the scene. His name is not yet being released.

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The two other riders noticed the third rider was missing and rode back to where the collision occurred, according to Barclay.

Intoxication is not believed to be a factor in the collision, he said.

Lucas Valley Road remains closed Thursday afternoon and is expected to reopen around 5:30 p.m., Barclay said.

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