Fire in Tahoe National Forest not as large as initially feared

Large plumes of smoke fill the air above Northern California at Emigrant Gap west of Truckee where the North Fire began Monday, Sept. 3, 2018, in Grass Valley, Calif. The fire is moving at a rapid rate of spread with large air tankers on order as reported by The Union. (Elias Funez/The Union via AP) less Large plumes of smoke fill the air above Northern California at Emigrant Gap west of Truckee where the North Fire began Monday, Sept. 3, 2018, in Grass Valley, Calif. The fire is moving at a rapid rate of ... more Photo: Elias Funez / Associated Press Photo: Elias Funez / Associated Press Image 1 of / 50 Caption Close Fire in Tahoe National Forest not as large as initially feared 1 / 50 Back to Gallery

Firefighters battling a blaze in a steep river canyon in Tahoe National Forest are counting on nine large air tankers and seven helicopters to halt the spread of the North Fire.

The wildfire erupted Monday near Emigrant Gap and consumed about 500 acres, authorities said Tuesday afternoon, forcing the Placer County Sheriff’s Office to empty and close several campgrounds. The California Highway Patrol also closed Interstate 80 ramps at Yuba Gap Road and Emigrant Gap Road.

Monday night’s estimate placed the size of the fire at 650 acres, but new observations made Tuesday with the aid of GPS led officials to reduce the scope of destruction.

The North Fire is just 10 percent contained, officialssaid, and no estimate for full containment have been projected.

The blaze is burning on both sides of the North Fork of the American River, fueled by brush and timber in the steep, rocky terrain of the river canyon.

The fire started around 4:30 p.m. in the North Fork campground, south of Emigrant Gap, according to the California Department of Forestry and Fire Protection, or Cal Fire.

It spread quickly and by Monday evening the Placer County Sheriff’s Office began evacuating the North Fork, Onion Valley and Tunnel Mills campgrounds on Texas Hill Road. The area around Lake Valley Reservoir was also evacuated, while the Sunflower, Lodgepole and Silvertip campgrounds were cleared.

Tahoe National Forest officials reported that hand crews, bulldozers and engines “worked through the night establishing an anchor point and starting to flank the fire.”

The cause of the fire remains under investigation, said Michael Woodbridge, a Tahoe National Forest district ranger.

Flames were first spotted near a popular campground and swimming hole, Woodbridge said, raising the possibility that human activity could have started the blaze.

Several wildland fires ignited up and down California over Labor Day weekend, Cal Fire spokesman Scott McLean said.

“But crews were able to jump on them quickly,” he added.

Two new fires were reported near Kelseyville in Lake County, but both were limited to fewer than 40 acres.

Here’s a quick look at some of the other wildfires in California:

• The Hirz Fire, in Shasta County northeast of Redding, has burned through 46,051 acres. It is 60 percent contained. Fire crews are working to extend containment lines on the northeastern edge of the blaze.

• The Ranch Fire, the larger of two fires to make up the Mendocino Complex, the state’s largest-ever blaze, has consumed about 410,000 acres in Lake, Mendocino and Colusa counties, and is about 98 percent contained.

Fire crews are focusing their efforts on the north and east ends of the fire as well as extinguishing islands of flame inside the containment lines. Full containment is expected Sunday.

• The Carr Fire, California’s most-destructive fire in 2018, was fully contained Thursday night after torching 1,079 homes. The inferno, which burned nearly 230,000 acres, and whipped through Redding subdivisions, started July 23. Firefighters remain in the area, patrolling the lines to make sure the fire stays contained.

Michael Cabanatuan is a San Francisco Chronicle staff writer. Email: mcabanatuan@sfchronicle.com Twitter: @ctuan