Around 34,500 buildings were threatened by the blaze, according to the multi-agency Inciweb information site.
Governor Jerry Brown declared the state of emergency for San Bernardino County, located just 60 miles (100 kilometers) east of Los Angeles, where the blaze, which has been named the Blue Cut fire, was quickly growing.
The fire, which began around 10:30 am (1730 GMT) Tuesday, has already burned more than 9,000 acres (3,600 hectares), according to Inciweb.
It poses "imminent threat to public safety, rail traffic and structures," according to the website, which said 82,640 people fell under an evacuation warning.
California is in its fifth year of a record drought and undergoing an extreme heat wave.
Two firefighters were lightly injured by the blaze, which some 700 fire personnel are battling, according to Inciweb.
Fire season is in full swing in California, where another fire has been burning 100 miles north of San Francisco since Saturday.
The Clayton Fire, as it is called, has burned more than 4,000 acres and is being fought by around 1,700 fire personnel who have brought some 35 percent of the blaze under control, according to the website Cal Fire.
More than 175 buildings have been destroyed as the blaze continues to move aggressively to the north, it said.
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