Communities have been told to evacuate as firefighters struggle to battle the blazes in the extreme conditions.
Two firefighters in Arizona died when their aircraft crashed while responding to a wildfire.
Meanwhile, Las Vegas matched its all-time temperature high of 47.2C (117F) on Saturday.
Firefighters battling the many wildfires in the region say the air is so dry that much of the water dropped by aircraft to quell the flames evaporates before it reaches the ground.
It comes just weeks after another dangerous heatwave hit North America, in which hundreds of sudden deaths were recorded, many of them suspected of being heat-related.
The region experienced its hottest June on record, according to the EU's Earth observation programme.
Experts say that climate change is expected to increase the frequency of extreme weather events, such as heatwaves. But linking any single event to global warming is complicated.
However, a study by climate researchers said the heat that scorched western Canada and the US at the end of June was "virtually impossible" without climate change.
More about: United-States
