A man rides his bicycle along a pier at Fort Baker in 100 degree heat Friday, Sept. 1, 2017, near Sausalito, Calif. Barely visible in the background is the San Francisco skyline. Dozens of cooling centers opened throughout California, schools let students out early and outdoor events were cancelled as temperatures soared from a heat wave expected to last through the Labor Day weekend. In normally cool and foggy San Francisco, temperatures reached 98 degrees Friday afternoon, well above the city's 90-degree record set for this day in 1950. (AP Photo/Eric Risberg)

SAN FRANCISCO - The Latest on heat and wildfires in the Western United States (all times local):

5:45 p.m.

Authorities say a fire burning near Yosemite National Park has entered a 2,700-year-old grove of giant sequoias.

California fire officials said Saturday the wildfire entered the Nelder Grove late Friday night.

Giant sequoias are among the largest and longest-lived organisms on Earth.

The Nelder grove holds 106 of them, including one of the world's largest, the 24-story-high Bull Buck sequoia.

It was unclear of any of the trees had been destroyed. California Department of Fire spokespeople say they have no new information on firefighters' efforts to save the grove.

Fire officials say the high number of already dead trees in the area is hampering their fight against the more than 8 square mile (20 square kilometre) wildfire.

Giant sequoia survive in only a few dozen scattered groves in Northern California.

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1:30 p.m.

San Francisco's transit system is cutting its speed to guard against possible heat-warped rails as the Bay Area breaks heat records for a second day.

The National Weather Service says the temperature in San Francisco reached 94 degrees even before noon Saturday, setting the heat record for Sept. 2. The city reached an all-time high of 106 degrees (41 degrees Celsius) Friday.

Forecasters are predicting more heat records throughout Northern California, with temperatures expected to climb as high as 115 degrees in some places.

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.

Trost says the rail system also has paramedics and air-conditioner technicians on standby during the heat wave.

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10:30 a.m.

Los Angeles Mayor Eric Garcetti says a wildfire burning through mountains just north of downtown is the largest in city history.

Only one home has burned and no one has been injured as the blaze grew to nearly 8 square miles and prompted evacuation orders for more than 600 homes in Los Angeles, Burbank and Glendale.

Heat that has afflicted the Western United States made conditions tough for crews in Los Angeles and beyond.

While temperatures could hit 100 degrees in the Los Angeles fire area, they're projected to peak even higher in Northern California.

In Sacramento, temperatures are expected to shoot past 110 on Saturday. Forecasters said areas inland from the San Francisco Bay Area could reach 115, a temperature last seen in 1950.

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9 a.m.

Firefighters in Los Angeles are working to contain a blaze that chewed through brush-covered mountains just north of downtown, growing to nearly 8 square miles and prompting mandatory evacuations for several hundred homes.

Los Angeles Fire Department spokeswoman Margaret Stewart said Saturday that no injuries have been reported and no buildings burned.

Heat that has afflicted the entire Western United States made conditions tough for crews, which had contained just 10 per cent of the brush fire by daybreak.

While temperatures could hit 100 degrees in the fire area, they're projected to peak even higher in parts of Northern California.

In Sacramento, temperatures are expected to shoot past 110 on Saturday. Forecasters said areas inland from the San Francisco Bay Area could reach 115, a temperature last seen in 1950.

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10:15 p.m.

The heat has peaked for Southern California, but parts of Northern California are set to see it soar some more.

Temperatures that reached 108 in Sacramento on Friday are expected to shoot past 110 on Saturday as a sweltering week continued.

Areas inland from the San Francisco Bay Area could reach 115, a temperature last seen in 1950, forecasters said.

San Francisco itself saw one of the hottest days in its history Friday at 106 but is now expected to recede into its usual cool-and-foggy summer pattern with dramatic temperature drops into the 80s then the 70s.

Triple-digit temperatures in the Los Angeles area are expected to drop into the 90s for the weekend, before falling more dramatically next week.

The weeklong heat wave generated by high pressure over the West extended up the coast and into the mountain states.

News from © The Associated Press, 2017