Firefighters responded Tuesday afternoon to a small brush fire near Soledad Canyon Road south of Agua Dulce. The Soledad fire started about 4:30 p.m., and by 4:50 p.m. had grown to 4 acres. It was running uphill and burning through light to medium brush with 3 to 5 mph winds pushing it north. No structures were threatened as of about 5 p.m. The Los Angeles County Fire Department has about 120 people responding to the fire, said Public Information Officer Brian Stevens. Thus far, the fire is burning in a state responsibility area, meaning the county has jurisdiction, Stevens said. The U.S. Forest Service was also responding, because the fire is near Angeles National Forest and the agency sends resources to fires that threaten forest land. At least one helicopter and two air tankers, with another on its way, are at the fire, said Nathan Judy, an Angeles National Forest spokesman. Because of the fire, the Metrolink AV Line 215 was holding near Acton. It was unclear how long the train would be delayed.