Firefighters battling a massive wildfire burning on the edge of the San Bernardino National Forest were preparing for the possibility that the blaze could join another wildfire and become even more difficult to control. By late Thursday, a 48,000-acre fire had destroyed more than 150 homes and buildings. While containment was at 20%, it was on course to possibly merge with the 8,200-acre fire in the national forest, where it could feed on vast stands of dead trees.