The Dragon Bravo Fire started on July 4 and was managed at first as a controlled burn. Then the wind picked up, and it quickly became uncontrollable.

Fire crews allowed a fire to burn through brush on the Grand Canyon’s North Rim. They they lost control.

The visitor center and a wastewater treatment plant were among the 50 to 80 structures lost, the park superintendent said. The area was evacuated Thursday.

What fueled the explosive growth of the Dragon Bravo Fire was a mix of gusty winds, dry air and above-normal heat – weather conditions experts described as atypical for this time of year, when monsoonal moisture typically tamps down wildfire risk across Arizona.

A water treatment facility at the North Rim had been compromised by the fire, causing chlorine gas to fall towards the bottom of the canyon.

ALBUQUERQUE, N.M. (AP) — U.S. land managers are racing the clock as hotter, drier weather raises the risk of wildfires in the nation’s overgrown forests with each passing year.