Firefighters burned off vegetation in the San Gabriel Mountains northeast of Los Angeles on Tuesday to protect historic Mount Wilson Observatory from a wildfire.
The Bobcat Fire was within 500 feet (152 meters) of the observatory by early afternoon and crews were waiting for it, the Angeles National Forest tweeted.
The blaze was just 3% contained after growing to more than 64 square miles (166 square kilometers) since breaking out Sept. 6.
The U.S. Forest Service said firefighters have been taking advantage of favorable weather to conduct firing operations to protect the observatory, nearby broadcast transmitters and communities on foothills below.
Mount Wilson rises to an elevation of more than 5,700 feet (1,737.3 meters) about 15 miles (24 kilometers) northeast of downtown Los Angeles.
The observatory played a pivotal role in early 20th century confirmation that galaxies exist outside the Milky Way.
In addition to its famed 100-inch (254-centimeter) telescope, the peak has other historic telescopes as well as modern astronomy instruments currently in use.
More than 16,600 firefighters are on the lines of more than two dozen major California wildfires that have scorched 5,000 square miles this year. Since the outbreak of massive fires on Aug. 15 there have been 25 fatalities.