SAN FRANCISCO (CBS SF/AP) — Much of the West was smothered in a blanket of heat Saturday with triple-digit temperatures hitting the Bay Area, Central and Southern California, Nevada, Arizona and New Mexico.

National Weather Service officials said the hottest days will be Saturday and Sunday, with temperatures rising as many as 10 to 15 degrees above the seasonal normal.

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Saturday afternoon temperatures reached 100 degrees in both Concord and Fairfield. Across the bay in San Francisco, thermometers broke the 90 degree mark in parts of the city.

Authorities warned people not to leave small children or pets in cars, where temperatures can quickly soar.

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Los Angeles and other cities were keeping libraries and other facilities open late to serve as cooling shelters for those without air conditioning.

Above-normal temperatures were expected through the weekend as a high-pressure system centered over New Mexico acted like a lid to block cooler air, leaving valleys, deserts and mountains high and very dry.

Phoenix broke a daily record Friday, reaching 117 degrees, and the expected Saturday high of 116 would top a 1992 record by 4 degrees, National Weather Service meteorologist Dan Leins said.

“Stay inside if you can,” he said. “It’s dangerous, regardless of how acclimated you are to the climate, because it can be deadly.”

Mike Stephens took precautions for an early-morning run in Estrella Regional Park, a desert and mountain wilderness area in Phoenix. He carried 1 1/2 liters of water and was careful not to overdo it.

“You have to know what your body can do,” he said.

In the desert 50 miles south of Phoenix Saturday afternoon Maricopa County Sheriff’s deputies rescued three migrants who had been out of water for at least three days. Teams were searching for about 17 others who were heading from the Mexican border north.

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The National Weather Service issued warnings of excessive heat throughout Southern California into Saturday night, with some areas expected to see highs of 10 to 15 degrees above normal, said Scott Sukup, a weather service meteorologist in Oxnard.

The mercury hit 96 degrees in downtown Los Angeles, with the San Fernando Valley and other inland valleys ranging up to 108. Palm Springs hit 116 and Death Valley’s high could reach 120 to 125, according to the weather service.

Highs of 110 to 112 were projected for Las Vegas and much of the Mojave desert.

The Western heat wave began Thursday and was expected to continue through Sunday.

“There’s been a big area of high pressure that was over New Mexico and it’s been expanding westward,” Sukup said.

The heat, coupled with low humidity, has increased the fire danger in California, where some two dozen major fires in recent weeks have destroyed thousands of acres of trees and brush left bone-dry by years of drought.

Winds were light “but it’s so hot and dry right now that it’s not going to take a lot of wind to spread fires,” he said.

Smoke from wildfires in Lake County and elsewhere blew into Northern California, bringing haze to at least four Bay Area counties Saturday and causing concerns for people with respiratory problems.

A brushfire that erupted Friday afternoon in forest foothills north and east of Los Angeles quickly grew to 4 square miles, torched several cabins and remained out of control Saturday. Firefighters worked in triple-digit heat and several were treated for dehydration or heat exhaustion.

Temperatures were expected to be cooler in California’s coastal regions, with highs in the 80s.

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