SAN DIEGO, Calif. -

Authorities say gunfire may have sparked a fire that scorched about 20 acres of dry brush in San Diego County.

Sheriff's Lt. Christine Robbins tells U-T San Diego that Border Patrol agents stopped a car leaving the area near the fire Saturday in Otay Mesa. She says the people in the car had been shooting guns.

The exact cause of the fire remains under investigation.

Cal Fire tankers and helicopters worked with ground crews to control the blaze sparked about a mile from a mile east of Richard J. Donovan Correctional Facility.

No structures were threatened.

Fire officials initially said the blaze had charred about 100 acres of brush in the first hour, but then scaled back their estimate to 20 acres.