A Southern California wildfire was roaring toward the historic Mount Wilson Observatory on Tuesday as an unprecedented fire season continued to rage across much of the West Coast, officials said.

The Bobcat Fire was within 500 feet of the observatory in Los Angeles County, which was founded in 1904 and once had some of the largest operational telescopes in the world, the U.S. Forest Service said shortly after 12 p.m.

“The #BOBCATFIRE is knocking on our door,” the observatory tweeted Monday night, noting that all personnel had been evacuated.

Images tweeted by the service Tuesday showed a massive plume of smoke rising from the San Gabriel Mountains north of Los Angeles, where the observatory is on a roughly 5,700-foot peak.

The fire, which ignited Sept. 6, had grown to more than 41,000 acres by Tuesday, the forest service said. Nearly 1,100 personnel were fighting the blaze.

The service said a C-130 aircraft was dropping thousands of gallons of retardant Tuesday afternoon to halt the fire’s spread. An image tweeted by the observatory showed a line of wildland firefighters crossing a suspension bridge from the century-old 100-inch Hooker telescope.

“We give our sincerest thanks to the firefighters who are on the ground defending our observatory as well as the pilots flying aircraft for fire suppression,” the observatory said.

The observatory is where the pioneering astronomer Edwin Hubble showed in 1925 that the Milky Way is one of many galaxies. Four years later, Hubble was at Mount Wilson when he confirmed that the universe is still expanding.

The Bobcat Fire is one of 25 major fires in California. A record 3.2 million acres have burned in California this year, and thousands of buildings have been destroyed. Twenty-five people have died, according to the California Department of Forestry and Fire Protection.

State officials have blamed a combination of climate change and a build up of dried-out vegetation for the dozens of fires that have scorched the state.

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Massive blazes have also raced across the Pacific Northwest, destroying towns and killing 10 people in Oregon and Washington.

Meteorologists said Tuesday that a haze settling over a wide swath of the East Coast was smoke that had made its way east from the fires.

The Associated Press contributed.