Hundreds of California residents fled their homes Saturday to escape a monster inferno being described as the largest in Los Angeles’ history.

Firefighters battled flames that chewed through nearly 8 square miles of brush-covered mountains as authorities issued mandatory or voluntary evacuation orders for more than 700 homes in Los Angeles, Burbank and Glendale.

The wildfires, just north of downtown L.A., had grown Saturday to the largest in city history, Mayor Eric Garcetti said. Three structures had burned, at least two of them homes, but fire officials were confident they could extinguish the fire unless winds picked up.

Garcetti declared an emergency and asked the governor to do the same so state and federal assistance would be provided quickly.

Wildfires also entered a 2,700-year-old grove of giant sequoia trees near Yosemite National Park and have driven people from their homes in Washington State, Oregon, Montana and other areas struggling with a weeklong heat wave that’s gripped Western states.

San Francisco, meanwhile, set a heat record for the day, hitting 94 degrees before noon. By mid-afternoon, it was 101 in the coastal city — hotter than Phoenix. With an all-time high of 106 on Friday, it became just the third time since the 1870s that San Francisco had back-to-back triple-digit days.

Temperatures reached 115 south of the city. It was a rare heat wave at a time of year that San Francisco residents usually call “Fogust” for its cloudy chill.

The region was so hot that officials with the Bay Area Rapid Transit system ordered trains to slow down on rails that were exposed to sun, expecting the heat would expand and possibly shift the metal track slightly, spokeswoman Alicia Trost said.

In Montana, a fire sweeping the Lolo Peak and Florence areas of the state grew to more than 41,300 acres as it continues to burn, KPAX reported. 

The fire, sparked by a lightning strike in mid-July, is being handled by 575 people assigned to the blaze.

“So yesterday the fire got established in the bottom of One Horse Creek and then started moving up the mountain and got up toward the top of the ridge. And then last night weather conditions became more favorable for burnout operations,” said Lolo Peak Fire Information Officer Derek Ibarguen. “And we conducted a burnout operation of about 50 to 60 acres that connected with the other burn blocks that have been in the past, to help shore up that eastern side of the fire.”

In Oregon, dozens of wildfires were sending up large plumes of smoke, causing disruptions in holiday travel as roads close and shutting down camping areas.

The wildfires forced about 140 hikers to shelter in place overnight Saturday on a popular trail about 90 miles east of Portland after they got stuck between two blazes.

The Oregonian reported a new fire ignited about 4 p.m. Saturday about a mile up the Eagle Creek Trail from the Eagle Creek Trailhead. Further up the trail, another fire was burning.

Fire spokeswoman Mary Huels said a crew of about 18 firefighters who had been assigned to the south end of the older fire as lookouts were keeping track of the people in the area and getting them to safe areas.

Search-and-rescue crews planned to help the hikers evacuate Sunday.

Three other hikers in a different areas nearby were rescued by helicopter Saturday evening.

In the Pacific Northwest, high temperatures and a lack of rain this summer have dried out vegetation that fed on winter snow and springtime rain. Officials warned of wildfire danger as hot, dry, smoky days were forecast across Oregon and Washington over the holiday weekend.

A fire about 80 miles southeast of Seattle has burned more than 23 square miles and led to new evacuation notices Saturday. About 3,800 homes were threatened, authorities said.

The weeklong heat wave was generated by high pressure over the West, the National Weather Service said.

The Associated Press contributed to this story.