A massive wildfire in Mariposa County triggered a new round of evacuations Tuesday as flames threatened power lines that feed Yosemite National Park, officials said.

Approximately 4,000 people have been forced from their homes since the Detwiler fire, which is burning east of Lake McClure, exploded to 25,000 acres, with hundreds of firefighters trudging through steep terrain to reach flames in overgrown vegetation, according to the California Department of Forestry and Fire Protection.

By 8:30 p.m., the blaze was only 5% contained and had destroyed eight structures, damaged one and was threatening an additional 1,500.

The Mariposa County Sheriff’s Office extended evacuation orders to residents in the town area of Mariposa, east of Merced.


The Red Cross opened evacuation shelters at Oakhurst Evangelical Free Church, Sierra Vista Presbyterian Church in Oakhurst and Cesar Chavez Middle School in Planada.

“The communities of Hunters Valley, Bear Valley, Catheys Valley, Mormon Bar, the town of Mariposa, Mount Bullion, Yaqui Gulch/ Agua Fria areas and Hornitos continue to be threatened,” CalFire said. “The fire encroaches on culturally and historically sensitive areas.”

Along the southern flank of the blaze, flames threatened power lines that supply Yosemite National Park, CalFire said.

Firefighters were facing volatile fire behavior, mostly due to dry, breezy and hot conditions, said meteorologist Christine Riley of the National Weather Service in Hanford.


Temperatures should cool by as much as four degrees Wednesday, but humidity will remain the same and windy conditions will persist.

Farther west, firefighting efforts in Saratoga were hampered Monday night by an unexpected drone sighting, said Ryan Cronin, chief fire investigator for Santa Clara County Fire Department. The 10-acre Eden fire erupted Monday afternoon near the Mountain Winery.

The drone was spotted about 7:40 p.m. as a water-dropping helicopter from CalFire prepared to douse the area, he said.

The pilot was forced to ground the copter “for fear of a midair collision” and abandon four water-dropping missions, Cronin said. Firefighters worked overnight to tamp down the flames.


“It really put them in a precarious position,” he said. “We didn’t appreciate that much.”

Fire officials later located and seized the drone, he said.

The department is investigating the incident.

Staff writer Alene Tchekmedyian contributed to this report.


veronica.rocha@latimes.com

Twitter: VeronicaRochaLA

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UPDATES:


11:45 p.m.: This article was updated with additional details about how many people have been evacuated.

10:05 p.m.: This article was updated with additional details about the size of the blaze and how many structures were destroyed and threatened.

This article was originally published at 2:15 p.m.