Inland areas north and east of San Francisco Bay were expected to bake in triple-digit heat of up to 115 degrees, and even the usually temperate coastline had 80s and 90s in the forecast. Temperatures in Sacramento were expected to shoot past 110.
A heat wave has hit Northern California on the U.S. West Coast since Friday, prompting temperatures to reach all-time highs in San Francisco.
Mayor Eric Garcetti told reporters the blaze, which broke out Friday and lit up the hills surrounding the northern suburb of Burbank overnight, had already burnt 5,000 acres (2,000 hectares), adding: "In terms of acres involved this is probably the largest fire in L.A. city history".
It burned near where a June wildfire came perilously close to hillside homes.
Bay Area Rapid Transit spokeswoman Alicia Trost says the rail line was reducing its speed until late Saturday because hot weather can expand and shift metal tracks.
"It's very unsettling", she said as she watched, already having packed her vehicle in case officials ordered her street to evacuate.
San Francisco on Saturday set a heat record for the day before noon, hitting 94 degrees.
The warmth extended up the West Coast and into mountain states, with excessive-heat warnings posted for southwest OR and lesser advisories in northwest Oregon.
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Henderson has four LPGA Tour victories, also winning the major KPMG Women's PGA past year and the Meijer LPGA Classic in June. Top-ranked So Yeon Ryu, playing alongside Thompson, missed the cut by a stroke with rounds of 74 and 70.
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.
A red flag warning for an increase in fire danger was also issued for parts of the region. Officials warned of wildfire danger as hot, dry, smokey days were forecast across OR and Washington over the holiday weekend.
- The blistering heat that has scorched the Bay Area for days is edging slightly down today, according to the National Weather Service.
Ice water stations were set up and dozens of people, many of them homeless, were taking shelter Friday.
"I work from home and I live in an old mobile home with no air conditioning and not very good insulation".
Forecasters said more heat could be expected when remnants of Tropical Storm Lidia move north from Mexico's Baja California during the weekend.
Managers of California's power grid asked for voluntary electricity conservation as forecasters predicted more extreme heat statewide.
Still, by 10 a.m., temperatures for many parts of the city were set to hit 80 degrees, triple digits were still possible later in the afternoon, and the September 2 heat record of 94 degrees was predicted to fall. Tens of thousands of people across the state were without power at various times Friday, though most outages didn't last long.