Forecasters say temperatures across much of California are expected to drop slightly over the weekend, although the Central Valley is still likely to see 37C (100F) heat.
"It's a little slower than we would like, but the heat is finally moving out," Kathy Hoxsie, a meteorologist with the US National Weather Service, told the Associated Press news agency.
Fresno County coroner Loralee Cervantes said her staff were trying to investigate at least 22 possible heat-related deaths.
Bodies were piled up in the mortuary's freezers, some on top of one another, she said.
"It's never been like this in my years here. This is really tragic," said Ms Cervantes.
Many of the dead were elderly who often were too afraid to leave their windows open, she said.
Emergency
California Governor Arnold Schwarzenegger has visited the Central Valley.
"As the record heatwave continues, we must protect our outdoor workers in the sweltering summer heat," he said.
Employers must ensure workers have access to shade and water during their shifts, under emergency regulations which are now permanently in force.
His office also stressed the need for people to take steps to avoid heat exhaustion and to look out for others, especially older people.
"A mobilised force of local workers will continue to knock on doors and make phone calls to protect our vulnerable residents who may be exposed to the relentless heat," a statement from the governor's office said.
Carcasses
The high temperatures over the past fortnight have led to the deaths of some 25,000 cattle in central California, about 1% of the state's dairy herd.
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Searing heat, soaring temperatures and prolonged power outages in San Jose have made life unbearable
"The timing is horrendous," Andy Zylstra, president of the California Dairy Campaign, told the French news agency, AFP.
"The price of milk is down 30% while feed, fuel, electricity prices are all up, and now we have these tremendous losses. It's just a kick in the head."
Several California counties have declared states of emergency because of the large number of carcasses that need to be disposed of.
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