An increasingly ominous fire sparked by lightning and burning all week in California’s Sequoia National Park has now entered the park’s Giant Forest, home to five of the world’s largest trees, including the largest, the General Sherman Tree.

Fire officials said Saturday that the intensity of the fire and the extent of the damage wasn’t yet known.

On Friday night, flames burned into the western edge of the Giant Forest along the Generals Highway, around four landmark giant sequoias known the Four Guardsmen, said Steven Bekkerus, public information officer for the U.S. Forest Service and other agencies battling the blaze.

“Those trees were affected,” he said. “We don’t know what the impacts are yet.”

Satellite heat images Saturday afternoon showed that flames appeared to also have moved into the area near the Giant Forest Village, Telescope Tree and other landmarks visited by millions of tourists, where trees tower up to 275 feet tall and date back 3,000 years.

“It’s really tough,” said Savannah Boiano, executive director of the Sequoia Parks Conservancy, a non-profit group that raises money for education, scientific research and other projects in the park. “I’m going to be candid. Millions of people go to this park every year. There are millions of memories made there every year. My heart is sad. This grove, this national park is so important to people throughout the world.”

Bekkerus said that firefighters have been wrapping some of the largest trees, including the General Sherman, which is 102 feet around at its base and 2,700 years old, in fireproof aluminum blankets for days, and also have more recently set up sprinklers in the grove to reduce the risk of fire danger.

Crews also have removed dead vegetation, shrubs and other materials that could increase the intensity of the fire, he said. They also lit some small fires in the iconic grove, home to 2,000 giant sequoias, to remove flammable material in anticipation of the main fire’s arrival.

“We were able to get in there and do burnout operations around some of the giant sequoias in the Giant Forest, including around the General Sherman tree,” Bekkerus said Saturday. “They’ve been making good progress. But we’ve been expecting the fire activity to pick up this afternoon.”

The National Weather Service issued a red flag warning for the Tehachapi mountains and Southern Sierra Nevada, south of Madera County, from 5 p.m. Saturday until 8 p.m. Sunday evening. Forecasters warned that a combination of very dry vegetation amid California’s ongoing severe drought, low relative humidity and gusty winds could contribute to extreme fire behavior.

Two fires in the park, the Colony Fire and the Paradise Fire, grew by nearly 6,500 acres between Friday and Saturday, to 17,857 acres. Both began with lightning strikes on Sept. 10. They merged Thursday night, approaching the Giant Forest, a landmark named by John Muir in 1875, from the west and south. Although there were 493 firefighters battling the fire, known as the KNP Complex, there was still 0% containment on Saturday afternoon.

The fire grew in intensity Friday, prompting commanders to withdraw crews from the Giant Forest for their safety. Complicating things, heavy smoke has limited when helicopters and airplanes have been able to fly overhead, dropping fire retardant and water from lakes.

“The fire started way up in high, rugged country where its just not accessible to firefighters,” Bekkerus said.

Sequoia National Park remains closed, and roughly 2,500 people have been evacuated in the community of Three Rivers on the park’s western edge as crews cut bulldozer lines on the park boundary to stop the fire’s spread.

Biologists have noted that the National Park Service has thinned brush and conducted controlled burns in the Giant Forest since the late 1960s and early 1970s, as a way to reduce the risk of a very hot, out-of-control fire burning there. But fires have been burning larger and hotter due to the drought, climate change and overgrown trees and brush in many parts of the West after 100 years of fire suppression.

Two other prominent giant sequoia groves in Sequoia and the adjacent Kings Canyon National Park — Grant Grove and Redwood Mountain Grove — also have had extensive thinning. But many of the 40 groves of giant sequoias elsewhere in the parks have not had such treatment and could be at risk if the fire continues to spread.

As of Saturday, fire had entered two other groves in the park, Suwanne Grove and Oriole Lake Grove.

Another wildfire 30 miles to the south, the Windy Fire, on Saturday had nearly doubled in size to 12,370 acres with 0% containment. It is burning on the Tule River Indian Reservation and in Sequoia National Forest in Tulare County.

There are roughly 70 giant sequoia groves in the world, all located in California’s Central and Southern Sierra.

By Saturday the Windy Fire had burned into at least three other giant sequoia groves. They included Long Meadow Grove, which was visited 21 years ago by former President Bill Clinton when he signed a proclamation establishing Sequoia National Monument at the area’s famous “Trail of 100 Giants.”

There, firefighters on Friday set up sprinkler systems.

Other groves where flames had entered in recent days include Peyrone North and South groves in Sequoia National Forest, Red Hill Grove, a 160-acre forest purchased for $3.3 million in 2018 by Save-the-Redwoods League, a San Francisco conservation group.

Last year, the Castle Fire killed between 7,500 and 10,600 giant sequoias, an estimated 10% to 14% of all the sequoias in the world, mostly in Sequoia National Forest. Then, 22 groves burned, about 10 of them severely. Biologists are now studying whether to replant some of those areas with giant sequoia seeds and saplings.

Boiano’s group has set up a fund to help restore the forests in Sequoia National Park at sequoiaparksconservancy.org. She said she is still holding out hope.

“The firefighters are working so hard for the best possible outcome,” she said.

A sprinkler system soaks giant sequoia trees along the Trail of 100 Giants in Sequoia National Forest on Saturday Sept. 18,2021 (Photo: Mike McMillan – Bureau of Indian Affairs)