VACAVILLE, Calif. (AP) — Wildfires raging through Northern California are threatening thousands of homes and blackening the skies near San Francisco as crews struggle to surround them despite steep terrain and blistering heat.

Fire officials say hundreds of thousands of acres and more than 100 buildings have burned, including homes.

At least 8,000 people were ordered to evacuate Wednesday night because of fires in the Russian River area of Solano County.

Other fires north, east and south of San Francisco on Thursday are causing horrible air quality over the city.

A pilot on a water-dropping mission died Wednesday when his helicopter crashed in central California.