North Rim, Grand Canyon
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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.
The NPS recommends avoiding hiking the Grand Canyon's inner trails between 10 a.m. and 4 p.m., when temperatures are at their peak. Temperatures in the inner canyon can reach over 120 degrees Fahrenheit in the shade, creating "extremely hazardous conditions for hikers," the NPS said.