The death occurred at a home near the town of Lyons, after a fire broke out Tuesday afternoon and consumed several buildings. It remains zero percent contained, despite the efforts of over 120 firefighters.
Firefighters discovered "human remains in one of the residences," Boulder County Sheriff Curtis Johnson said.
"I can confirm for you that we do have one fatality associated with this fire," he added, without providing further details.
At 1,550 acres (630 hectares), the so-called "Stone Canyon Fire" is far from the largest of the dozens currently scorching the western United States.
Fires are raging across the region, in a summer that has brought successive, intense heat waves that have dried out vegetation to create tinder-dry conditions.
California, Oregon and Washington states have been particularly affected.
In California, the Park Fire has swelled to 390,000 acres burnt, making it the fifth-largest conflagration in the state's history by area affected.
Reinforcements have been sent from as far as Texas to help control the blaze, which is 18 percent contained.
It was allegedly sparked last week by a man pushing a burning car into a ravine, according to local prosecutors, who have charged the suspect with arson.
The massive fire has forced the evacuation of thousands of people from a region around 100 miles (160 kilometers) north of state capital Sacramento.
Vast clouds of smoke have reached neighboring states.
Further south, in central California, firefighters on Wednesday were also battling a large blaze in the Sequoia National Forest, home to world-famous giant sequoia trees.
A slight drop in temperatures has helped with efforts to combat both fires in recent days, but a new heat wave is expected to sweep across the American West from Thursday.
On Tuesday, California Governor Gavin Newsom urged people to remain extremely vigilant, with months of high fire risk still ahead in a region where climate change has lengthened the fire season to almost year-round.
"Remember (...) it's not just August, September and October, but likely November, December, that we'll be fighting the ferocity of Mother Nature and these fires," he told a press conference.
Repeated heat waves and extreme weather events are accelerated by climate change, which is linked to humanity's reliance on fossil fuels, according to scientists.
