As lightning-sparked wildfires expanded Saturday in southern Mariposa County and Yosemite National Park, firefighters were bracing for the possibility of thunderstorms that could ignite more blazes.
The Oliver fire, about 14 miles southeast of Mariposa, has grown to 2,306 acres with only 40% containment, Cal Fire reported. That is more than 100 acres larger than on Friday.
In Yosemite National Park, the Star fire is still burning eight miles southeast of Wawona. It has grown to 200 acres from 160 acres a day before, and firefighters have not reported any containment.
Those fires are among hundreds started by dry lightning storms across Central and Northern California last weekend. Smoke has contributed to poor air quality throughout the central San Joaquin Valley.
The National Weather Service said an unstable air mass could trigger thunderstorms today from Yosemite National Park to the Kern County line.
Storms were possible anywhere in the northern Sierra Nevada or the northern Central Valley on Saturday night, said National Weather Service forecaster Johnnie Powell in Sacramento.
But the front was expected to pass by today, setting up a second week of abysmal air quality.
Statewide, more than 17,000 firefighters, 1,500 fire engines and bulldozers, and more than 80 helicopters and aircraft were involved in battles against more than 1,000 fires.
The wildfires in Northern California have turned the air into an unhealthy stew of smoke and ash. Health advisories urging residents to stay indoors and limit exposure to the smoky air were issued Saturday from Bakersfield north to Redding, a distance of nearly 450 miles.
President Bush issued an emergency declaration for California on Saturday and ordered federal agencies to assist in firefighting efforts in many areas. Gov. Schwarzenegger had made the request Friday.
The fires have destroyed 47 structures and injured 85 people and continue to threaten nearly 10,000 homes, businesses and buildings, according to the California Department of Forestry and Fire Protection.
A lightning-sparked wildfire in the Big Sur region of the Los Padres National Forest has burned 42 square miles and destroyed 16 homes. The blaze, which was only 3% contained, has forced the closure of a 12-mile stretch of coastal Highway 1 and driven away visitors at the peak of the tourist season.
In Mariposa County, the Oliver fire was moving north and northeast within the Devil's Creek drainage in steep, inaccessible terrain, said Cal Fire spokesman Craig Tolmie. The battle to contain it involves 1,307 people, he said.
A dozen homes along Aurora Road and Standard Mill Road remained under an evacuation order, Tolmie said. Another 35 homes in the 5100 to 6100 blocks of Chowchilla Mountain Road are under an evacuation warning.
No structures have been damaged in the weeklong blaze, but it has cost about $4.7 million to fight the fire so far, Tolmie said. Firefighters were able to fully contain a dozen other fires in the Sierra National Forest. Three wildfires -- the Silver Knob, Westfall and Chiquito fires -- burned more than 725 acres.
Firefighters also mopped up about nine smaller wildfires in the Sierra National Forest.
Unstable weather in the southern Sierra Nevada, however, had firefighters fearing more lightening strikes. "Hopefully, it won't happen," said Bob Miller, a volunteer officer for Cal Fire.
An unhealthy air alert for Fresno, Madera, Kings, Tulare, Kern, Merced, Mariposa and Tuolumne counties will be in place until 11 a.m. Monday, the National Weather Service said.
Today, everyone -- but especially children and the elderly -- should stay indoors in areas where they can see or smell smoke, authorities said. Exposure to particulate matter can cause asthma attacks, aggravate lung disease and increase the risk of respiratory infection, air quality officials said.
Meteorologist Gary Sanger of the National Weather Service said strong winds are needed to dissipate the smoke. "But I don't see that happening any time soon," he said.