On Labor Day 1971, two professors from Northern Arizona University conducted a study of the noise level at the South Rim of the Grand Canyon. At that time, air traffic was allowed to fly over the area. "Noise levels at this once tranquil vacation spot now rival levels on a busy downtown street."
The peak at times was 90 decibels. The tests were performed on the South Rim, near Phantom Ranch, and along two inner canyon trails. "Researches said there was no time, from dawn to dusk when they did not hear the sound of an aircraft flying over the canyon."
Thanks to Grand Canyon Historical Society for this history.
