The pitched battle to protect the mountaintop observatory and an adjacent communications site came as power equipment belonging to electric utility Southern California Edison came under scrutiny in an investigation into the cause of the so-called Bobcat Fire.
Since Sunday U.S. Forest Service officials pushed back the estimated time for full containment from Oct.15 to October 30.
Creating "dozerlines" is a firefighting technique in which bulldozers remove plants and other flammable material to leave a line of bare soil and stop the fire from spreading.
All personnel from the observatory were evacuated due to the wildfire.
While no structures have been lost from the Bobcat Fire, threats from the blaze remain significant, with containment lines established around just 3 per cent of its perimeter, Mr Clearwater said. "Fire officials predicted that the fire would approach Mt. Wilson from Echo Rock. It looks like they are correct".
By Tuesday night, the Angeles National Forest praised the firefighters' work around the mountain.
This aerial footage was shared by the Southern California Air Operations, who said it was filmed on Tuesday.
"The recent Ranch 2 Fire, Fish Fire and the 2009 Station Fire are helping to slow fire progression, however the Bobcat Fire continues to burn north and east where there is no fire history in the last 80 years and in the San Gabriel Wilderness", the Forest Service said.
Meanwhile, evacuation warnings remained in the cities of Duarte, Bradbury, Monrovia, Arcadia, Sierra Madre, Pasadena and Altadena, which stand along the foothill of Santa Ana Mountain where the Angeles National Forest is located.
In 1924, astronomer Edwin Hubble used the larger of the two telescopes to confirm theories that galaxies exist beyond the Milky Way and by 1929, was able to show, along with colleague Milton Humason, that the universe was expanding.
A smoke advisory is in effect through Sunday in most of Los Angeles County and parts of Orange, Riverside and San Bernardino counties due to the Bobcat Fire burning in the Angeles National Forest that has blackened 29,245 acres and remains only 6% contained. "Luckily we don't have any wind driving it now".
The blaze was one of dozens of wildfires that broke out during the Labour Day holiday weekend, stoked by a late-summer heat wave that baked much of the US West Coast before cooler weather prevailed.