The wildfire, which sent smoke billowing down the foothills toward large suburban houses, comes amid hot weather and fierce Santa Ana winds blowing in the region that had already prompted the National Weather Service to issue a wildfire-related "red flag" warning for much of the area.
The so-called Etiwanda Fire marks one of the first major wildfires of the year in Southern California, and comes just ahead of the hotter months between, May and October, when the blazes most frequently break out.
The blaze broke out in the San Bernardino National Forest at about 8 a.m. and quickly spread across 800 acres, driven by winds of up to 80 miles per hour (129 km/h), which is extremely gusty for the region, officials said.
Television news footage showed bright orange flames in the brush, near towers for power transmission lines. Parents and students rushed away from local schools enveloped in smoky air, their hair and shirts flapping in the wind.
The blaze east of Los Angeles prompted authorities to issue mandatory evacuation orders for an area in northern Rancho Cucamonga that has 1,100 homes and 2,500 people living in them, said U.S. Forest Service spokesman Chon Bribiescas. Rancho Cucamonga is a largely middle class suburban city.
Officials have deployed 30 fire engines against the blaze, according to wildfire tracking site InciWeb. But because of the high winds, officials have not been able to deploy aircraft to fight the fire.
California officials have kept staffing levels for wildland firefighters at elevated levels since last year because the state is in the midst of its worst drought in decades.
Governor Jerry Brown has issued emergency proclamations related to the drought, calling on residents to avoid washing their cars and watering their lawns.
