This picture taken on July 26, 2015 shows a child playing in a fountain on a square to cool himself amid a heatwave in Binzhou, eastern China's Shandong province.   CHINA OUT     AFP PHOTO        (Photo credit should read STR/AFP/Getty Images)
STR/AFP/AFP/Getty Images
This picture taken on July 26, 2015 shows a child playing in a fountain on a square to cool himself amid a heatwave in Binzhou, eastern China's Shandong province. CHINA OUT AFP PHOTO (Photo credit should read STR/AFP/Getty Images)
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RESTRICTED TO EDITORIAL USE  / MANDATORY CREDIT:  "AFP PHOTO / Josh EDELSON" / NO MARKETING / NO ADVERTISING CAMPAIGNS /  DISTRIBUTED AS A SERVICE TO CLIENTS  ==        (Photo credit should read JOSH EDELSON/AFP/Getty Images)
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(CNN) —  

Four people have been killed in a record-setting heat wave that’s plaguing the Southwest.

A handful of raging wildfires have also popped up in New Mexico, California and Arizona.

The fatalities were all in Arizona, but temperatures of 120 degrees will be possible in the desert Southwest early this week, the National Weather Service reported.

On Monday a new fire, dubbed the “Reservoir Fire,” quickly grew and now along with an adjoining fire has consumed 3,500 acres in the Angeles National Forest outside Los Angeles. The blaze sent enormous plumes of smoke into the sky while being battled by the Los Angeles County Fire Department and the U.S. Forest Service.

The two fires are expected to merge Monday night and authorities have dedicated 350 personnel on the ground and aircraft to fight the flames, which so far have not moved toward houses. Two helicopters equipped with night vision will continue to work through the night.

Elsewhere in California, evacuations were ordered in San Diego County as fires continue to rage near the U.S.-Mexico border. And a large wildfire in Santa Barbara County also forced mandatory evacuations.

02:06 - Source: CNN
Firefighters battle California wildfire blaze

At least three large wildfires are burning in Arizona, covering 65,000 acres, while two more in New Mexico have consumed 53,000 acres, the InciWeb reported.

Three large fires are raging in New Mexico, Arizona and California:

  • Dog Head Fire in northern New Mexico: 17,891 acres burned and 9% contained as of Sunday night
  • Cedar Fire in Arizona: 26,739 acres burned and 40% contained as of Monday morning
  • Sherpa Fire in California: 7,893 acres burned and 51% contained as of Monday morning

The record-setting heat is another source of danger.

Arizona authorities were still searching Monday afternoon for a hiker who was still missing Monday. who went missing in Ventana Canyon while hiking with two companions on Sunday, Tucson.com reported. One of his partners hiked to safety while a search party found the second man dead about four miles from the trailhead.

The rescue effort in Ventana Canyon was one of three major rescue efforts conducted Sunday. A woman from out of state also died Sunday in Arizona’s Pima County due to the heat, according to sheriff’s spokeswoman Courtney Rodriguez.

A 28-year-old woman hiker died Sunday in Phoenix, according to Larry Subervi, a Phoenix Fire Department spokesman. And on Saturday a 25-year-old male hiker died, he said.

Monday saw little relief in terms of scorching temperatures, which set records Sunday:

  • Santa Fe’s high of 102 degrees tied its hottest all-time temperature on record (from June 27, 2013, although there are gaps in its record).
  • Tucson’s high of 115 degrees tied its third hottest temperature of all time.
  • Yuma’s high of 120 degrees tied for its fourth hottest day recorded.
  • Phoenix’s high of 118 degrees tied for its fifth hottest day.

It’s the hottest start to summer ever in three states – California, New Mexico and Arizona – according to CNN Meteorologist Pedram Javaheri. More than 30 million people are under heat warnings or advisories.

It was so hot in Phoenix Sunday that a Mesa Airlines flight to the city had to be diverted back to Texas, the airline said.

Seven areas in western and central New Mexico broke heat records in addition to 14 places in California – where Palm Springs, Thermal, Indio and Borrego all saw temperatures 117 degrees or higher.

The following map from the National Weather Service shows the parts of the United States that are currently under heat advisories (pink areas face excessive heat warnings, while areas in orange face heat advisories).

Much of the current heat wave can be attributed to a so-called heat dome – a pattern that can lead to record-setting temperatures and heat waves – according to CNN Meteorologist Rachel Aissen. A heat dome occurs when air is capped by the upper atmosphere in the same location: The air hits the cap and returns to the surface, continuing to heat it like a convection oven.

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CNN’s Joe Sutton, Cheri Mossburg, Artemis Moshtaghian, Dave Alsup, Dave Hennen and CNN Meteorologists Pedram Javaheri and Rachel Aissen contributed to this report.