Firefighters struggled against rugged terrain, high winds and an August heat wave Tuesday to slow the spread of the biggest wildfire ever recorded in California, an inferno that exploded to be nearly the size of Los Angeles in just 11 days.

The 450-square-mile (1,165-square-kilometer) blaze, centered near the community of Upper Lake, about 100 miles (160 kilometers) north of San Francisco, spread fast because of what officials said was a perfect combination of weather, topography and abundant vegetation turned into highly flammable fuel by years of drought.

Firefighting efforts were also initi...