San Dimas

Approximate location where a motorcycle and a big rig collided in San Dimas. (Google Maps)

A fatal collision between a big rig and motorcyclist in San Dimas closed part of the 10 Freeway and backed up traffic for miles during the Monday morning commute.

The collision, reported at 4:27 a.m., occurred on the westbound 10 Freeway near the Kellogg Drive exit, according to California Highway Patrol Officer Monica Posada.

Investigators were trying to determine what caused the crash, which killed the motorcyclist,  ABC News reported.

A SigAlert was issued for the westbound 10 Freeway between Highway 57 and Kellogg Drive. At one point, all lanes were closed, causing a 10-mile backup.

The two left lanes were reopened by 7 a.m., but westbound traffic remained jammed from Ontario.

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angel.jennings@latimes.com

Twitter: LATangel