Corpses piled up at the morgue Thursday, and aid workers went door-to-door, checking in on elderly people in hopes of keeping the death toll from California's unprecedented 12-day heat wave from rising.

In Fresno County's morgue, the walk-in freezer was stuffed with bodies, with some piled on top of others, said Coroner Loralee Cervantes. With limited air conditioning, employees worked in sweltering heat as they investigated at least 22 possible heat-related deaths.

"It's never been like this in my years here," Cervantes said. "This is really tragic."

California coroner's offices said the number of deaths possibly connected to the heat wave rose to 90.

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The mercury dropped slightly in some areas, with Sacramento expected to get its first double-digit high in 12 days, but Fresno and Bakersfield were expected to hit 109.

In Stanislaus County, which includes Modesto, officials were investigating whether sizzling temperatures were responsible for 20 deaths. Salvation Army workers walked door-to-door to check on elderly and other vulnerable residents.

Kern County was investigating eight possibly heat-related deaths. Among the victims were two Bakersfield brothers who were found dead in their beds in a home without air conditioning.

Gov. Arnold Schwarzenegger announced that California was making 75 cooling centers available to residents at fairgrounds statewide. Health officials also were contacting nursing homes to make sure they had evacuation plans in place in case their air conditioning failed, he said.

State Sen. Dean Florez called on Schwarzenegger to declare a state of emergency in the Central Valley, noting that residents — and hundreds of cows — were dying each day.

"Record-breaking heat requires a record-breaking response," Flores said. "The conditions, staying this hot for this long, are simply too much for the most vulnerable residents."

July has seen extreme heat across the country. In St. Louis, the misery was worsened by storms that knocked down power lines last week in the worst blackout in city history. Most of the 12 Missouri deaths attributed to the heat wave occurred in the St. Louis area, where about 36,000 homes and businesses remained without power Thursday afternoon.

Missouri regulators opened an investigation into whether AmerenUE and other utilities were properly prepared for the storms, and whether they responded adequately.