A 17,000-acre blaze continued to burn Thursday at Camp Pendleton, moving in two directions as it gobbled up chaparral on the sprawling Marine base bordering Orange County. The Horno Fire is one of three that broke out in the area early Wednesday. The other two were quickly contained. Cpl. Alec Kleinsmith, a base spokesman, said the blaze was nearly 50 percent contained Thursday morning. Despite having one of the highest containment percentages of the fires in the county, firefighters remain worried about the Horno blaze because it has two active heads -- one northbound following Basilone Road and the other southbound following Aliso Canyon Road. Smaller fires had prompted the California Highway Patrol to temporarily close Interstate 5 as firefighters moved in, but all lanes were eventually reopened. Train service through the area also was suspended. Kleinsmith said one of the other two blazes, dubbed the Margarita Fire, charred about 200 acres. The third fire broke out near the commissary and blackened about 5 acres. Both were contained Wednesday. Basilone Road was closed from San Onofre to Stage Coach Road, and the Las Pulgas Gate and Las Pulgas Road were closed, he said. Stuart Mesa Road was closed from Edson Range to Las Pulgas Road.