Firefighters toiled in stifling heat on the lines of destructive bushfires across the US West, making progress against some blazes while struggling to tame others that have forced evacuations of hundreds of homes.

In heat-stricken Southern California, powerful winds that sent an overnight inferno hopscotching through the Santa Barbara County community of Goleta vanished in the morning, allowing firefighters to extinguish smoldering ruins of an estimated 20 structures, including homes.

"It's really given us a good opportunity to get in there and get some work done," said county fire Captain Dave Zaniboni.

The fire's spread was stopped at about 40.5 ha or less and teams were working on an accurate tally of damage in the neighbourhood, where some houses were in ruins while homes next door were intact.

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Eric Durtschi stood outside his destroyed house, where a burned-out car stood in the driveway and kids' bicycles were strewn about.

Durtschi, his wife and six children had left Utah and moved in just a few weeks ago. He said he hadn't yet told his two oldest children their home was gone. He managed to collect his severely burned vintage guns, hoping to salvage them.

A neighbour's home across the street was spared. The man had stayed through the night spraying down other people's houses.

Elsewhere in Southern California, firefighters increased containment of a central San Diego County fire that rapidly spread over 162ha, destroyed 18 structures and damaged eight, and a wildfire in the San Bernardino National Forest was holding at 404 ha and forced evacuation of about 700 homes in the mountain community of Forest Falls.

Fires also burned on the Marine Corps' sprawling Camp Pendleton base in northern San Diego County.

The Southern California fires erupted as strong high pressure over the West spawned an epic heat wave that saw parts of Los Angeles suffer in temperatures up to 47.2C. There was little relief overnight.

"Temperatures at 8 am were ridiculously over 100 degrees (37C)" in foothills near Forest Falls and many inland valleys, the National Weather Service said.

Firefighters battle flames at the Alpine Oaks Estates mobile home park. Photo / AP
Firefighters battle flames at the Alpine Oaks Estates mobile home park. Photo / AP

Forecasters said the region's siege of heat would gradually ease today, but the unstable air mass unleashed downpours that triggered flash-flood warnings for the mountains northeast of Los Angeles.

Further up north and just south of the California-Oregon border, the 88sq km Klamathon Fire in rural Siskiyou County was just 5 per cent contained. The body of a resident was found in the ruins of a home, among 15 destroyed structures tallied so far.

Authorities described "extreme fire behaviour with movement in multiple directions," with threats to the California communities of Hornbrook and Hilt as well as Colestin, Oregon. Ray Haupt, chairman of the county Board of Supervisors, said losses included homes and livestock.

Elsewhere in California, the 357sq km County Fire northwest of Sacramento was nearly 50 per cent contained. Ten structures were counted destroyed but damage assessments were continuing.

With fires occurring statewide, a Colorado-based Boeing 747-400 supertanker was deployed to California.

In Utah, meanwhile, authorities allowed the return of some residents who fled a fire near a popular fishing lake 130km southeast of Salt Lake City. The blaze has burned about 193 sq km and destroyed 90 structures, including homes, cabins, sheds and garages, since starting Sunday in the mountains.

In Colorado, firefighters took advantage of occasional rainstorms to extend their containment lines at several large fires.

- AP