"We are extremely heartbroken for this loss", Mendocino Complex incident commander Sean Kavanaugh said, adding that officials will release more information as it becomes available.
When asked about the claims by left-wing environmental groups and even US lawmakers who blame climate change for contributing to the fires, Zinke said that is a separate matter from the need to manage forests to help lessen the spread of wildfires or even prevent them.
More than 30,000 personnel, including firefighters from across the United States and almost 140 from Australia and New Zealand, were battling the blazes that have consumed more than 1.6m acres (648,000 hectares), according to the National Interagency Coordination Center.
Another massive blaze, the Carr Fire, has blackened about 207,000 acres and killed eight people in and around Shasta County, north of Sacramento near the OR state line.
Per a Cal Fire tweet: "After a father informed his daughter that her fish was likely dead, both were in for quite a shock when they returned home to a well-fed fish!"
Forrest Gordon Clark, 51, was charged with aggravated arson and criminal threats, among other crimes, for allegedly starting the fire. As it has grown to cover more than 202,000 acres, 1,077 homes, 22 commercial structures and 500 other buildings have burned. He's being held on $1 million bail, and faces a maximum sentence of life in prison if convicted.
On Sunday, the California Department of Forestry and Fire Protection confirmed that the fire, which has destroyed approximately 1100 residences, has spread over 816 square kilometres and is 61 per cent contained. The fire is burning near the Mendocino National Forest, about 140 miles northwest of Sacramento.
After a month of burning, the Ferguson Fire has singed 96,457 acres across three national forests and private land.
Yosemite National Park will reopen Tuesday, 14 days after a wildfire choked the park with smoke at the peak of tourist season.