A woman has died after collapsing while hiking and mountain biking during a record-breaking heatwave in Phoenix.
Fire officials said the 28-year-old started biking with two friends and stopped breathing a few hours later. Crews said her condition appeared to have been heat-related.
The woman, an avid hiker and personal trainer who had no known medical issues, was flown to hospital where she died.
The National Weather Service said temperatures hit 118F, breaking a record of 115F for June 19, set nearly 50 years ago
Portions of Arizona and south-east California are expected to keep getting scorched with a high pressure ridge lifting out of Mexico. The weather service forecast temperatures will drop to 113F on Tuesday and stay below 115F for the rest of the week.
Phoenix did not reach 120F as forecasters said was possible, but Yuma, in the south-west corner of Arizona, did. National Weather Service meteorologist Andrew Deemer said he had "no doubt there are places in the Valley that hit 120F or so".
The woman's death came a day after a 25-year-old Phoenix man died of heat exposure while hiking in neighbouring Pinal County.
In California, the districts of Burbank and Glendale, just north of central Los Angeles, soared past 100F, the National Weather Service said. Burbank saw a record 105F.
That heat was no help to firefighters who had to work to put out a wildfire in a Los Angeles neighbourhood, where densely packed homes were briefly in danger.
Further north west in the San Fernando Valley, some thermometers were reading close to 110F, and Palm Springs in the inland desert hit 115F.
The heat spurred state regulators to urge residents to voluntarily cut their consumption of electricity, but it has not yet brought the rolling blackouts that southern Californians have been told to expect this summer after a massive natural gas leak.
Crews beat back the blaze in the Silver Lake neighbourhood of LA after it damaged two homes, destroyed three sheds, scorched yards and sent trees up in flames.
Neighbours scrambled with garden hoses and buckets, while water-dumping helicopters and scores of firefighters chased embers and doused steep hillsides to keep the flames from spreading.
The blaze only charred eight acres, but it put urban residents on alert to the hot, dry conditions that have helped wildfires spread rapidly across more remote places from the California coast to New Mexico.
A fire that has burned 12 square miles west of Santa Barbara stayed in check, but firefighters braced for the return of gusts that fanned the flames earlier in the week, threatening hundreds of homes and leading to evacuations of popular coastal campgrounds.
In New Mexico, a 28-square-mile fire that erupted last week and destroyed 24 homes in the Manzano Mountains south of Albuquerque was largely uncontained, but higher humidity allowed crews to strengthen lines around the fire and keep a lookout for hot spots where flames could jump the line.
In eastern Arizona, a fire that has burned 19 square miles south west of Show Low advanced south, but containment increased to 40%.
Meanwhile, a new wildfire forced the evacuation of hundreds of people from a small town in the California desert near the Mexico border.
State fire officials said the blaze had surged to nearly 1.5 square miles amid triple-digit temperatures.
An evacuation was ordered for the community of Potrero, a town of about 600 people along State Route 94, a few miles north of Tecate, Mexico, and about 40 miles south east of San Diego.
The Red Cross has opened two community centres and a primary school for evacuees.