REDDING, Calif. (AP) - Fire officials say a wildfire roaring through timber and brush on both sides of a Northern California highway tripled in size overnight, prompting mandatory evacuations. The U.S. Forest Service said Thursday the blaze burning along Interstate 5 near Redding had grown to 23 square miles (60 square kilometers). It was 8 square miles (21 square kilometers) on Wednesday. Officials did not immediately say how many people the evacuation order affected. The fire is in a rural area with scattered homes. Officials said the blaze was human-caused but they didn't indicate whether it was arson or accident. Truckers abandoned their vehicles as flames roared up hillsides. Officials say about 17 big-rigs were abandoned and at least four caught fire. A wildfire nearby that was only contained last week left neighborhoods in ruins and killed eight people.