By Ian Simpson

(Reuters) - Fire warnings were in place across three western U.S. states on Sunday as record-breaking heat threatened to feed wildfires that have blackened thousands of acres (hectares), especially in California and New Mexico.

The National Weather Service said temperatures of 120 Fahrenheit (49 Celsius) were possible in southwestern deserts through Wednesday.

"Red flag warnings" for potential fires covered an area stretching across southern California, southern Nevada and southern Arizona.

"These extreme temperatures can be life-threatening," the weather service said on its website. The high temperatures have joined with a prolonged dry spell to worsen the fire threat.

The agency declared an elevated threat in California's Santa Barbara County from dry conditions and evening winds. More than 2,000 firefighters there are battling the so-called Sherpa Fire, which had burned 7,811 acres (3,161 hectares) in coastal canyons.

Firefighters estimated the fire was 45 percent contained. The Sherpa Fire broke out on Wednesday and has forced mandatory evacuations in some areas.

Another blaze, the Dog Head Fire, southeast of Albuquerque, New Mexico, has destroyed about two dozen homes and forced evacuations.

Almost 1,000 personnel were fighting the blaze that has burned through about 17,615 acres (7,129 hectares) of timber and logging zones.

In Alaska, a fire warning was also in place for the eastern part of the Alaska Range, with winds forecast to gust to 60 miles per hour (96 km per hour).

Saturday's high temperature was 112F (44C) at Death Valley, California, the weather service said.

(Reporting by Ian Simpson in Washington; Editing by Andrew Bolton)