Ash rained down across Los Angeles on Sunday from a destructive wildfire that the mayor said was the largest in city history.
The fire was one of several blazes that sent thousands fleeing homes across the US West during a blistering holiday weekend heatwave.
In Oregon, about 140 hikers were awaiting rescue early on Sunday after being forced to spend the night in the woods after fire broke out along the popular Columbia River Gorge trail.
Search and rescue crews air-dropped supplies on Saturday as flames prevented the hikers' escape.
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 Montana and other areas struggling with a week-long heatwave that has gripped the region.
In Washington state, Governor Jay Inslee proclaimed a state of emergency across all counties as three major fires closed recreation areas and prompted evacuations in a mountain town just south-east of Seattle.
Los Angeles Mayor Eric Garcetti declared a local emergency and asked the governor to do the same after a wildfire in densely populated hillside areas destroyed three homes.
Hundreds of firefighters battled flames that chewed through nearly eight 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.
Los Angeles resident Tracy Goldman had her car packed in case officials ordered her street to evacuate.
"It's very unsettling," she said as she watched flames that had reached within 200 feet of her house.
Tourists snapped shots of their planes landing against a backdrop of orange flames in the hills near Hollywood Burbank Airport.
San Francisco on Saturday set a heat record for the day before noon, hitting 94 degrees.
By the 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 heatwave at a time of year that San Francisco residents usually call "Fogust" for its cloudy chill.
The weekend also broke heat records in wine counties north of San Francisco, where Labour Day for some vineyards marks the start of the busy grape harvest.
"We had been hoping for a mellow season," Kat Doescher, senior winemaker at Madrone Estate Winery outside Sonoma, said shortly after sunrise. "But I look at the forecasts, and I see a heatwave that's not getting any cooler."
Fires up and down California's Sierra Nevada and further to the north-west cast an eerie yellow and grey haze. In the Sierra foothills, authorities opened a centre where evacuated residents could find out whether their home was destroyed in a blaze about 70 miles north of Sacramento.
Another wildfire burning near Yosemite had grown to 8.5 square miles and entered the Nelder Grove of 106 giant sequoias, despite firefighters' efforts to stave it off.
Giant sequoias are among the largest and longest-lived organisms on Earth, and survive naturally only in Northern California.
Fire officials said they had no immediate information on whether any of the giant trees - including the 100-foot-round, 24-storey-high Bull Buck sequoia - had burned.
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, smokey days were forecast across Oregon and Washington over the holiday weekend.
A fire about 80 miles south-east of Seattle has burned more than 23 square miles and led to new evacuations. About 3,800 homes were threatened, authorities said.
Dozens of wildfires in Oregon were sending up large plumes of smoke, causing disruptions in holiday travel and shutting down camping areas.
The weeklong heatwave was generated by high pressure over the West, the National Weather Service said.
Forecasters said more heat could be expected when remnants of Tropical Storm Lidia move north from Mexico's Baja California during the weekend.