(CNN) -- Firefighters gained ground in recent days in the battle with a wildfire that burned 84 buildings and blackened 28,000 acres of dense forest in northern California.
The Ponderosa fire, which is in a remote area of Shasta County, California, is just one of 42,750 wildfires that have burned 6,901,035 acres in the United States this year, according to the National Interagency Fire Center.
The fire, ignited by lightning five days ago, was 57% contained by Thursday, allowing some families forced from their homes to return, fire officials said.
The Ponderosa fire still threatens 900 homes, forcing those residents to evacuate. Nearly 2,500 people, equipped with 263 firetrucks and 11 helicopters, are involved in the effort to stop the Ponderosa fire.
Shasta is one of three northern California counties for which Gov. Jerry Brown has declared states of emergency because of wildfires this week. The other counties included in the declaration, which makes emergency funding available to fight the blazes, are Plumas and Tehama.
In Plumas County, the Chips fire has burned 63,147 acres, most of it in the Plumas National Forest. The 1,146 personnel fighting it have managed to gain 40% containment, according to officials.
"Today's mission is clear: hold, hold, hold," Operations Section Chief Rob Laeng told firefighters at their morning briefing Thursday.
In Tehama County, the battle is almost over against the Mill fire. It is 95% contained after 1,680 acres burned, according to the California Department of Forestry and Fire Protection.
A fire that has burned nearly 100,000 acres, mostly managed by the U.S. Forestry Service, in northern Idaho is still just 5% contained three weeks after it began, officials said. The Trinity Ridge fire threatens the community of Featherville, but efforts to create a buffer for the area have been "very successful," according to a statement on the fire's incident website.