FACTBOX-California's lightning-sparked fires among state's biggest

California's lightning-sparked wildfires more than doubled in size into some of the largest in state history on Friday, forcing over 175,000 people to flee their homes. Here are some facts about the fires racing across counties in the San Francisco Bay area and central California that have killed six people since Aug. 15.

771,000 - acres burned 540 - structures destroyed

175,000 plus - people evacuated over 12,000 - Firefighters deployed

nearly 12,000 - Number of lightning strikes 1,204 - Square miles the fires cover

2.3 million - Acres destroyed by fires so far this year 4.7 million - Number of acres destroyed last year

(Sources: California Department of Forestry and Fire Protection and National Interagency Fire Center) (Compiled by Bill Tarrant and Andrew Hay; editing by Grant McCool)