The wildfire, nicknamed the Valley Fire, has spread rapidly to span about 25,000 acres (10,117 hectares) since it erupted on Saturday afternoon in Lake County, north of San Francisco, the California Department of Forestry and Fire Protection (Cal Fire) said on its website.
Early on Sunday morning, local media showed footage of several structures ablaze in Middleton, a small community of about 1,500 residents, one of several that were ordered to evacuate by the Lake County authorities on Saturday, Reuters reported.
Four firefighters, who had been dropped off by helicopter, suffered second-degree burns as they built containment lines, said Cal Fire spokesman Daniel Berlant.
The firefighters were airlifted to UC Davis Medical Center in Sacramento where they were listed in stable condition, Berlant later said on Twitter.
About 100 miles (161 km) to the southeast, the so-called Butte Fire has destroyed 86 homes and 51 outbuildings in rural Amador and Calaveras counties, where it covers an estimated 65,000 acres (26,305 hectares), officials said. It is only 15 percent contained.
Thousands of residents in the area were required to evacuate on Friday, and the blaze threatened more than 6,000 structures, officials said.
More than 3,800 firefighters were working to contain the fire, which erupted on Wednesday near the former gold mining town of Jackson.
Flames from a larger blaze, dubbed the Rough Fire which is burning in Kings Canyon National Park in central California, had forced officials to order about 3,500 to evacuate by Friday, said Jim Schwarber, a spokesman for the team handling the blaze.
Firefighters on Saturday intentionally set low-intensity fires in a famed grove of giant sequoia trees in Kings Canyon National Park to remove vegetation and protect the grove from the wildfire, Schwarber said. The giant sequoias themselves are naturally flame-resistant, officials said.
More than 2,900 firefighters were on the front lines of the blaze on Saturday, with containment listed at 29 percent, officials said.
Ranking as California's largest active fire, the Rough has scorched about 128,800 acres (52,000 hectares).
A firefighter watches a tree burn as the Butte fire rages near San Andreas, California September 12, 2015.