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.

Bystanders immediately initiated CPR while NPS medical personnel and volunteers responded on foot, according to park officials.   Attempts to resuscitate the man were unsuccessful, NPS said.

A hiker has died on the South Kaibab Trail in the Grand Canyon National Park while attempting to reach the Colorado River.