Reuters: Firefighters worked to contain some 400 wildfires burning across Northern California on Sunday as the state baked under a fourth day of an early summer heat wave that has strained the power grid and left residents wilted. One structure was destroyed and 150 homes were evacuated near Fairfield, 40 miles (64 km) southwest of Sacramento, in the path of the worst of the fires, which blackened more than 3,500 acres (1,416 hectares) in wine-producing Napa County. "The weather …