(CBS SF) – A shipping-and-receiving building was damaged in an early morning fire at Skywalker Ranch today, a Marin County fire battalion chief said.

The fire was reported just after 4 a.m. at the 4,000-acre ranch off of Lucas Valley Road south of Novato. The ranch, owned by filmmaker George Lucas, houses the headquarters of Lucasfilm and Skywalker Sound.

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The sprinkler system went off, which helped firefighters extinguish the flames quickly, Battalion Chief Mike Giannini said.

A fire brigade based at the ranch initially responded to the blaze before Marin County firefighters arrived, he said.

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The building contains office furniture and supplies, and its roof was damaged, he said. The total damage is estimated at about $25,000 Giannini said.

The cause of the fire is under investigation.

No injuries were reported.

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