By Madison Park and Dakin Andone, CNN

(CNN) -- A week after several wildfires ignited in Northern California, firefighters are making progress toward containing the massive blazes that have killed at least 40 people and burned about 5,700 structures.

On Sunday, diminished winds gave firefighters a break in the weather to gain ground on the rash of fires that have scorched swaths of Northern California, including Sonoma and Napa counties.

As California Gov. Jerry Brown said over the weekend: "We are not out of the woods yet, there's still fires burning."

Officials voiced cautious optimism over the latest efforts.

"Overall, things are feeling optimistic for us," said Bret Gouvea, deputy chief of California Department of Forestry and Fire Protection (Cal Fire), during a Sunday briefing. "We're very cautious about that. As you know, we have a lot of fires across Sonoma County."

More than a dozen fires are burning in California -- most of which are in Northern California.

But in a sign of some relief, a number of residents are being allowed to return home as mandatory evacuation orders lifted in areas, including the cities of Napa and Calistoga.

Latest developments

The Sonoma County Sheriff's Office identified four more victims on Sunday. They were all over the age of 70. They are: Lee Chadwick Roger, 72, of Glen Ellen; Sharon Rae Robinson, 79, Daniel Martin Southard, 71, and Carmen Colleen McReynolds, 82, all of Santa Rosa. A total of 22 people have died in Sonoma County.

An estimated 217,000 acres have burned, according to a Sunday update from Cal Fire.

Approximately 75,000 people have been evacuated, Cal Fire said Sunday.

The 50,000-plus acres Atlas fire in Napa and Solano counties was 65% contained as of Sunday.

The Nuns fire in Sonoma County had consumed more than 48,000 acres and was 40% contained.

The Tubbs fire in Sonoma County, which spread to nearly 45,000 acres, was 60% contained.

'We're turning the corner'

The outbreak of wildfires has become one of the deadliest in the state's history, according to Cal Fire.

More than 200 people are reported missing. Entire subdivisions and neighborhoods have been incinerated, leaving behind ash, debris and scorched earth.

In Sonoma County, damages are expected to cost upwards of $3 billion, tweeted State Sen. Mike McGuire, who represents the North Bay.

Despite fire officials' more optimistic tone about getting the flames under control, trouble spots still exist.

Gouvea from Cal Fire warned that some fires are "just fighting us... They're not going easy, but we're getting them."

Firefighting resources and crews came to California from all over the country and even Australia, according to Cal Fire.

"We're turning the corner," Gouvea said Sunday. "You're seeing containment levels coming up. Things feel good in our gut as firefighters. So we just need weather to cooperate with us a little bit."

In a promising forecast, there's a chance of rain later this week in the affected areas. A system from the Gulf of Alaska is expected to bring rain Thursday morning, according to a tweet from the National Weather Service for the San Francisco Bay Area.

Ash and debris could be 'very toxic'

Meanwhile, authorities are also planning for evacuees to return home.

"Over the next 24 hours you'll see a lot of repopulation plans coming out," Gouvea said, adding that authorities will "phase those repopulations in" so residents don't all attempt to return at once, causing traffic congestion and possibly safety hazards.

Napa County is switching gears and turning its focus toward recovery, said county supervisor Belia Ramos.

Health officials advised residents heading back to damaged or burned down homes to be careful about sifting through their belongings.

"The ash and the debris is very toxic. You have lots of chemicals and plastic and paint burned down," said Dr. Karen Relucio, public health officer in Napa County.

She advised that it could be hot and there could be sharp objects in the debris.

"We strongly urge you not to remove any large debris because this can release toxins into the air," she said.

In Santa Rosa, a city about 50 miles northwest of San Francisco, Penny Wright was one of those who returned.

She tearfully walked through the debris of where her home once stood. With burned cars, concrete and twisted metal scattered everywhere, it was hard to tell which one was her house.

"All your life savings and work for all the years is gone," she said. "We lived here 10 years. I never thought that Santa Rosa would have a fire like this and we would lose everything."