By Joseph Serna, Los Angeles Times (TNS)

California Gov. Jerry Brown declared a state of emergency Friday for Northern California counties hit by wildfires, and officials announced that a U.S. Forest Service firefighter had died on the front lines in Modoc County.

David Ruhl, a South Dakota firefighter who had been working in California for several weeks, died Thursday while fighting the Frog fire, according to a statement on InciWeb. Few details were immediately provided, but the statement said Ruhl’s body was found by search and rescue personnel.

“This loss of life is tragic and heartbreaking,” Forest Supervisor Amanda McAdams said in the statement. “Please keep the family and all of our Forest Service employees in your thoughts and prayers during this difficult time.”

Officials are investigating how Ruhl died.

Late Friday, Brown issued a statement from himself and wife, Anne, saying they “were saddened to learn of the tragic death” of Ruhl, “who left his home state to help protect one of California’s majestic forests…. We extend our deepest condolences to his family, friends, and colleagues with the U.S. Forest Service.”

The Frog fire has burned 800 acres near Adin, California, in the northeast corner of the state.

The U.S. Forest Service said it was lowering its flags to half-staff in Ruhl’s memory. The announcement came shortly after Brown declared the state of emergency.

“California’s severe drought and extreme weather have turned much of the state into a tinderbox,” Brown said in a statement. “Our courageous firefighters are on the front lines and we’ll do everything we can to help them.”

The declaration will allow faster deployment of resources to the fire zones, including the National Guard, if that is deemed necessary.

The state of emergency came as a fast-moving fire north of Napa Valley continued to grow Friday and new evacuations were ordered for residents in a nearby rural town, authorities said.

The Rocky fire grew to 18,000 acres and was 5 percent contained, according to a tweet from Daniel Berlant, a spokesman for the California Department of Forestry and Fire Protection. The Lake County Sheriff’s Department issued a mandatory evacuation for Jerusalem Valley residents before 10 a.m., after the blaze moved north and jumped a road.

About 650 residents have fled their homes since the blaze began Wednesday afternoon.

Water-dropping aircraft and firefighters on the ground have been working around the clock to douse the flames and dig a containment line around the blaze, according to Cal Fire. The Rocky fire began at 4:10 p.m. Wednesday near Morgan Valley and Rocky Creek roads, 62 miles north of Napa, and traveled quickly, spreading into heavy brush and woodlands, Cal Fire said.

Firefighters were still assessing the damage caused by the massive blaze, but officials said the flames have so far destroyed three structures and multiple outbuildings.

The blaze is one of 18 large wildfires burning in California, requiring the deployment of nearly 8,000 firefighters.

In response to the wildfires, the National Guard mobilized nine helicopters to help state firefighters. Authorities are worried that thunderstorms forecast for the weekend could trigger dry-lightning strikes and more blazes.

On Thursday, a fire swept through an Isleton mobile home park, destroying seven mobile homes and forcing residents to flee. A small vegetation fire in the Solano County delta town got out of control and reached the homes before firefighters could quell the flames.

“We don’t have a hydrant system out here, so once our apparatus runs out of water, we have to rely on water from river drafting, which takes up a little bit of effort setting that up,” Assistant Chief of the River Delta Fire Department Jessie Rosewall told Fox 40.

Photo: Los Angeles county firefighters battle wild land fire in Wrightwood, California, July 17, 2015. REUTERS/Gene Blevins