A wildland fire in the Sierra foothills grew to 2,151 acres Friday, forcing the evacuations of 1,650 people as it threatened scores of structures, officials said. The Trailhead fire started Tuesday afternoon along the Middle Fork of the American River, in steep and hard-to-reach terrain near Todd Valley in El Dorado and Placer counties, roughly 130 miles northeast of San Francisco. Despite the rough terrain firefighters managed to make progress surrounding the fire with large containment lines on several sides. In Placer County, crews were able to complete and bolster containment lines Thursday night to prevent fire spread to Peachstone Gulch and the community of Todd Valley. While the fire remained a good distance from any homes or businesses in both Placer and El Dorado counties, Villemaire said mandatory evacuations were ordered for nearby communities as a precautionary measure and to make room for all of the fire suppression equipment needed. “The fire is moving into more favorable terrain, moving to ridges, flatter terrain and roads, where they can have a more advantageous angle to fight the fire,” she said.