The blaze was considered 6% contained by Thursday evening, after breaking out Sunday afternoon near the Cogswell Dam and West Fork Day Use area of the forest. The U.S. Forest Service estimates the fire will not be fully contained until Oct. 15.
The blaze continued to roar through tinder-dry brush Thursday and doubled in size in 24 hours to nearly 24,000 acres, and it jumped Highway 39. Residents have been told to be ready to go if conditions take a turn, but officials say despite the dramatic flames seen burning above communities, the fire was moving in the opposite direction.
The fuel filled the air with smoke and ash miles from the fire lines, creating some of the worst air quality in 30 years.
The South Coast AQMD issued a smoke advisory for Thursday impacting most of Southern California. Smoke and ash from the Bobcat and El Dorado fires were to blame for the poor air quality Thursday in Southern California.
RELATED: Southern California wildfires cause worst air quality in 30 years
Bobcat Fire Evacuations
Several foothill communities near the Bobcat Fire are under an evacuation warning.
Monrovia residents were warned of potential evacuations on Monday, and the warning was then expanded to include the communities of Arcadia, Duarte, Bradbury, Sierra Madre, Pasadena and Altadena.
A "voluntary evacuation suggestion" by the city of Arcadia for residents north of Foothill Boulevard and east of Santa Anita Avenue was lifted about 5:30 p.m. Wednesday by city officials, who said the fire had "generally progressed away from" Arcadia.
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For residents still impacted by the evacuation warning, officials ask they have an evacuation plan in place and be ready to leave with necessary supplies and personal belongings. Vehicles should be fully fueled and facing out in driveways to be ready to leave immediately if mandatory evacuations are required.
Evacuations were previously ordered for residents and Angeles National Forest visitors from Big Santa Anita Canyon, Mt. Wilson, San Gabriel Canyon and Monrovia Canyon, but by Wednesday evening no evacuation orders were in effect, according to the U.S. Forest Service.
The American Red Cross said it closed an evacuation point at Santa Anita Park on Thursday, and it will continue to provide virtual assistance. Those impacted by the Bobcat Fire and in need of help can contact the local Red Cross via the Disaster Distress Hotline at 800-675-5799. The Red Cross said it has teams on standby to reopen the evacuation site if needed.
The Fairplex in Pomona and Santa Anita Park are providing shelter to large animals. At least 300 horses can be sheltered at the Fairplex.
California fire map
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Los Angeles County park closures
The county has closed the following parks through the weekend because of poor air quality:
Eaton Canyon Natural Area
Devil's Punchbowl Natural Area
Frank G. Bonelli Regional Park
Lario Staging Area
Marshall Canyon Regional Park and Nursery
Peck Road Water Conservation Park
San Dimas Canyon Natural Area
Santa Fe Dam Recreation Area
Forest and road restrictions
All 18 national forests in California, including the Angeles National Forest, are closed due to the fire conditions across the state, the U.S. Forest Service said Wednesday.
"The number of large fires and extreme fire behavior we are seeing across the state is historic," regional forester Randy Moore said in a news release. "These temporary closures are necessary to protect the public and our firefighters, and we will keep them in place until conditions improve and we are confident that national forest visitors can recreate safely."
USFS shut down eight national forests in the southern half of the state earlier in the week.
Highway 39 was closed at Canyon Entrance Station. The Angeles Crest Highway is closed from 10.6 miles east of La Canada-Flintridge to Islip Saddle.
RELATED: USFS closes all 18 national forests in California amid 'unprecedented and historic fire conditions'
Battling the blaze
The fire was moving in a northeasterly direction Thursday, and 540 firefighters were working to extinguish the flames, according to the Forest Service. No structural damage or injuries have been reported.
"The northern portion of the fire has reached up into ridges near Angeles Crest Highway where retardant drops have been made,'' the Forest Service said. "Steep terrain and dry fuels, some of which haven't burned in the last 60 years, will create challenges for crews.''
On Friday morning, "areas south of the Bobcat fire along the I-210 corridor from Pasadena to Rancho Cucamonga will likely see the highest levels (of particulate matter) as smoke is likely to remain closer to the ground overnight,'' the South Coast AQMD advises, while on Friday afternoon, onshore winds are expected to move smoke east and northeast toward the San Gabriel Mountains and San Bernardino Mountains.
"Priority is to contain the south end of the fire in anticipation of Santa Ana winds," the Forest Service reported.
Earlier in the week, officials were concerned winds would bring flames closer toward homes, but winds were not as strong as predicted.
The cause of the fire is under investigation.
City News Service contributed to this report.