MANITOU SPRINGS, Colo. >> Searing, record-setting heat in the interior West didn’t loosen its grip on firefighters struggling to contain blazes in Colorado, Utah and other Rocky Mountain states.

Colorado has endured nearly a week of 100-plus degree days and low humidity, sapping moisture from timber and grass, creating a devastating formula for volatile wildfires across the state and punishing conditions for firefighters.

“When it’s that hot, it just dries the fuels even more. That can make the fuels explosive,” said Steve Segin, a fire spokesman for the U.S. Forest Service.

Much of Nevada, Utah, Wyoming and Colorado are under a red flag warning, meaning conditions are hot, dry and ripe for fires.

For the fourth straight day, Denver cleared 100 degrees and reached a record high temperature of 105 Monday. Other areas in the state have also been topping 100 degrees, including northern Colorado where the state’s second largest wildfire in history is burning.

And the scorching heat doesn’t appear to be letting up soon. Temperatures across Colorado are expected to clear 100 degrees again today. Segin said such prolonged heat is “extremely taxing” physically on firefighters, who are working long days and carrying heavy gear.

The wildfires are also posing a threat to tourism.

Several large wildfires across the West have placed some tourist destinations from Montana to New Mexico in danger just at the height of midsummer family road-trip season, putting cherished Western landscapes at risk along with hordes of vacationers.

U.S. Forest Chief Tom Tidwell told The Associated Press in a phone interview Monday that about half of the nation’s firefighting personnel who are usually assigned to large fires are working in Colorado right now.

“It’s just because it’s so dry,” Tidwell said. “They saw very low snowpack, especially in that lower country. Hot, dry winds with dry fuels, you get the ignition, and this is what we see.”