SUISUN CITY (CBS SF) — A large vegetation fire was burning dry grass fields and destroyed at least one structure in Suisun City, according to authorities.

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The fire was first reported at about 4:15 p.m. in a rural area near 533 Bella Vista Drive just east of Fairfield. It reached three alarms a short time later.

Shortly after 5 p.m., The fire was encroaching onto Travis Air Force Base property. Firefighting crews from the base also assisted in fighting the fire.

Video from Chopper 5 showed firefighters trying to contain the fire consuming fields of grass along the road. A heard of cows was seen running along the edge of the fire before running across an area of field that had already burned.

Two outbuildings — a shed and a trailer that was used as an office building — were completely destroyed, but officials noted that the buildings were abandoned and scheduled to be torn down anyway.

As of about 7 p.m., officials said the fire had consumed approximately 45 to 50 acres. Firefighters said the fire appeared to have started near a cluster of homes.

Crews were continuing to work to contain the fire Thursday evening. While firefighters were trying to mop-up the fire and put out hot spots on public land as of 7:15 p.m., there was no word on the level of containment reached on Travis AFB.