SAN FRANCISCO (NYTIMES) - After growing explosively to become California's largest wildfire so far in 2022, a blaze in the foothills of the Sierra Nevada moderated on Sunday (July 24), with firefighters able to defend communities a dozen kilometres from Yosemite National Park.

The Oak fire was ignited and spread swiftly on Friday.

It has burnt about 6,800 hectares and still could threaten 3,300 homes and businesses.

As of Monday morning, seven structures had been destroyed - an earlier estimate had said there were 10 - and more than 3,000 residents had been ordered to evacuate.

Cal Fire, the state's main firefighting agency, said in a statement on Sunday night that firefighters had made "good headway" against the blaze and that protective clearing by fire crews is shielding the small communities of Lushmeadows and Mariposa Pines.

"The fire continued to be active, but yesterday afternoon it did slow and moderate," Capt. Jon Heggie, a battalion chief at Cal Fire, said on Monday morning. "But the potential for it to grow still exists, and we will continue to fight this fire aggressively."

Cal Fire said it expects full containment by Saturday, a hopeful sign for a blaze that seemed out of control just a few days ago.

The effects of the fire could be felt hundreds of kilometres away, as winds pushed smoke northwards along the Sierra Nevada foothills, resulting in unhealthy air readings.

For now, air quality forecasts suggest that onshore winds will most likely keep ground-level smoke away from the San Francisco Bay Area and Sacramento over the next couple of days.

However, the smoke may stay high in the atmosphere and cause skies to appear hazy.

Officials advised residents to check air quality readings, especially those sensitive to pollution.

The fire closed a highway leading to Yosemite, which is still recovering from the Washburn fire.

That blaze started this month and at one point threatened the park's Mariposa Grove of sequoias, some of the world's oldest trees. The Washburn fire is now all but extinguished.

The Oak fire is by far the largest wildfire in the state so far this year, besting the Washburn fire, which burnt about 1,980 hectares, according to a tally by Cal Fire.

However, July is still early in the state's traditional fire season, which runs through the summer and well into autumn, when the threat rises of more potentially lethal wind-driven wildfires.