A blazing sun silhouettes power lines in North Long Beach ahead of the Labor Day weekend's historic heat wave. <span class="copyright">(Luis Sinco / Los Angeles Times)</span>
A blazing sun silhouettes power lines in North Long Beach ahead of the Labor Day weekend’s historic heat wave. (Luis Sinco / Los Angeles Times)

An epic Southern California heat wave crested Sunday with numerous all-time high temperature records set, including a 121-degree reading in Woodland Hills that marked a historic milestone for Los Angeles County.

The broiling temperatures put extreme pressure on the power grid, with malfunctions leaving thousands without power and officials warning that rolling blackouts could affect millions of customers.

It also fueled a series of fast-moving brush fires across the region, including one in Angeles National Forest near Duarte that broke out Sunday afternoon and forced Labor Day weekend visitors to flee.

In San Bernardino County, the El Dorado fire near Yucaipa had burned more than 3,000 acres and forced evacuations in some communities. To the south in San Diego County, the Valley fire in the backcountry had burned 5,300 acres and destroyed at least 10 structures.

The Woodland Hills reading of 121 degrees broke the county’s old record of 119 degrees set in July 2006 and was one of several records to fall Sunday. Escondido achieved an all-time high of 115 degrees, shattering a record set in 1909. Paso Robles also hit an all-time high at 117, as did Idyllwild (104) and Chino (121).

Woodland Hills is one of the hottest parts of Los Angeles and often records extreme temperatures. But Sunday’s conditions — measured at a station at Pierce College — marked the highest temperature from an official National Weather Service station in not only L.A. County but also Ventura, Santa Barbara and San Luis Obispo counties.

The weather service said Riverside hit its highest temperature ever for September at 117 degrees; Santa Ana hit a record high for the day at 106.

Officials have warned people to avoid outdoor activities even as temperatures cool slightly Monday.

A woman in her late 40s was hiking on a trail in the Santa Monica Mountains in Calabasas when she began to feel sick and collapsed at 2 p.m. Saturday, said L.A. County Sheriff’s Deputy Juanita Navarro.

She was pronounced dead at the scene. The official cause of death is still unknown, Navarro said.

Because of the dangerous heat wave, all trails in the Santa Monica Mountains are closed through Labor Day, Malibu Search and Rescue said in a tweet.

In Angeles National Forest, the Sheriff Department search and rescue team performed an air rescue Saturday on a semiconscious hiker suffering from heat exhaustion on the popular Strawberry Peak trail, where temperatures often soar because it has minimal shade in the afternoon.

Blackouts could take place during peak evening hours, from 5 to 9 p.m., according to the California Independent System Operator, which runs the power grid for much of the state.

That could force utilities to cut off power to 2.5 million to 3 million customers statewide, Eric Schmitt, vice president of operations for California ISO, said Sunday at a news briefing.

California ISO was urging consumers to conserve energy, particularly during the peak demand time of 3 to 6 p.m.

“I think it’s fair to say that without really significant conservation and help from customers today that we’ll have to have some rolling outages,” Schmitt said. “So this is really an appeal for people to help us out to get through what will prove to be a very, very difficult day.”

The organization declared a statewide emergency, which lasted about 2 1/2 hours, after a transmission line carrying power from Oregon to California and another in-state power plant went offline unexpectedly, according to the organization. The cause of the outages was unknown as of Sunday evening.

California ISO said Sunday evening via Twitter that no outages were ordered by grid operators because Californians conserved enough energy. 

If blackouts should occur, Southern California will notify affected customer via phone, text message and email as soon as possible, said Reggie Kumar, a spokesman for Southern California Edison.

“We know that people are working from home and kids are doing online learning, so we understand how disruptive these outages can be,” he said. “If directed by CAISO, we will try to make sure they are as short as possible with the least impact on any one group of customers.”

The outages typically last an hour and affect a neighborhood, not an entire community, Kumar said.

As of Sunday afternoon, much of Southern California Edison’s 18,000-plus reported outages were in Los Angeles County, where more than 10,000 customers were without power. The largest outages as of 2:30 p.m. Sunday included 1,203 in Inglewood and 1,126 in Paramount.

The outages were heat- and non-fire-related, Kumar said, but overall, the electricity distribution system was performing well.

As of Sunday afternoon, the Los Angeles Department of Water and Power had enough power supplies and did not anticipate the need to implement rolling blackouts, a DWP spokesman said.

The utility did experience some small power outages in West Adams, Reseda, Sun Valley and Pacoima, among other places. As of Sunday morning, about 7,000 customers were without power, and crews had worked around the clock to restore power to 37,000 after temperatures and energy demand soared, according to the utility.

Pacific Gas & Electric Co. warned that the Diablo wind event set to hit Monday evening through midday Wednesday may require public safety power shutoffs for about 103,000 customers in the Sierra foothills, North Bay and East Bay. PG&E provides electricity across Northern and Central California.

The hot weather has hampered firefighting and heat-related rescue efforts across the state.

In the Sierra National Forest northeast of Fresno, the 45,500-acre Creek fire trapped more than 200 hikers in the Mammoth Pool recreation area when it crossed the San Joaquin River on Saturday afternoon, prompting a massive rescue effort by the California National Guard.

In Los Angeles County, the Bobcat fire started Sunday afternoon and quickly grew to 1,000 acres near the popular West Fork Picnic Area, a usually peaceful, wooded area where many residents fish and swim in the cool San Gabriel River.

California Department of Forestry and Fire Protection officials said Sunday evening that the El Dorado fire had a rather bizarre cause: a smoke-emitting device that was part of a gender-reveal party in a Yucaipa park. Such devices generally produce blue or pink smoke to signal the gender of an expected child.

“Cal Fire reminds the public that with the dry conditions and critical fire weather, it doesn’t take much to start a wildfire,” the agency said in a statement.

Times staff writers Thomas Curwen in Los Angeles and Rong-Gong Lin II in San Francisco contributed to this report.

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