LITTLETON, Colo. >> A wildfire burning in Colorado’s heavily populated Front Range region has burned dozens of homes and outbuildings, while a second fire crept within a quarter-mile of evacuated homes near Denver on Thursday.

Authorities said they were hopeful that hundreds of threatened homes could be saved. But firefighters working in the tree-covered foothills on the eastern edge of the Rocky Mountains faced sweltering temperatures, and some were sidelined by heat exhaustion.

The struggle to contain the blazes came after authorities said Wednesday that a person was killed in a wildfire west of Lyons, Colorado. The person’s remains were found inside one of five houses that burned.

Almost 100 large fires are raging across the West. The largest, in Northern California, has burned more than 400 houses and other structures, officials reported.

New, large fires were reported in Idaho, southeast Montana and north Texas.

About two dozen homes and outbuildings were damaged or destroyed in a wildfire, near Loveland, Colorado, authorities disclosed after an initial survey of the burn area.

Meanwhile the Quarry Fire southwest of the Denver suburb of Littleton encroached on several large subdivisions after people in 600 homes were ordered to evacuate.

By Thursday afternoon, firefighting aircraft zipped back and forth between the blaze and a nearby reservoir. Planes skimmed the surface to scoop up water and hovering helicopters pumped water into their tanks before returning to the fire to dump their loads.

Jim and Meg Lutes watched from an overlook near their house northeast of the fire as smoke plumed up from the ridges. Their community west of Littleton was not under evacuation orders, but the couple had been ready to start packing a day earlier when flames could be seen blanketing the mountains.

“It can come over that hill pretty quick if the wind changes,” said Jim Lutes, 64, pointing to a nearby ridge.

Five firefighters were injured Wednesday, including four who had heat exhaustion, said Mark Techmeyer, a spokesperson with the Jefferson County Sheriff’s Office.

The fire was in steep terrain that made it difficult to access but had been held to less than one square mile with no houses yet destroyed, authorities said. It remained a major hazard, with hot temperatures and low humidity elevating the danger.

The fire was discovered Tuesday night by a deputy on patrol in what authorities described as “open areas.” It was small at first but quickly spread.

“I think anytime that you see a small fire in an area like that at 9:00 at night, it makes you scratch your head a little bit,” Techmeyer said at a Wednesday briefing when asked if he thought the fire was suspicious.