I am always amazed to find yet another huge mystery associated with the Grand Canyon or Arizona, for that matter, that I hadn't heard of previously. This time the story seems to originate from a front page story in the Phoenix Gazette of April 5, 1909 entitled "EXPLORATIONS IN GRAND CANYON Mysteries of Immense Rich Cavern being brought to light Jordan is enthused Remarkable finds indicate ancient people migrated from Orient." There are dozens of online articles and blog posts about the rumored underground city. Although the article attributes the whole investigation to the Smithsonian Institute, which organization denies any involvement.
Here is a quote from the Gazette article so you can get the flavor of the story:
Under the direction of Prof. S. A. Jordan, the Smithsonian Institute is now prosecuting the most thorough explorations, which will be continued until the last link in the chain is forged. Nearly a mile underground, about 1480 feet below the surface, the long main passage has been delved into, to find another mammoth chamber from which radiates scores of passageways, like the spokes of a wheel. Several hundred rooms have been discovered, reached by passageways running from the main passage, one of them having been explored for 854 feet and another 634 feet. The recent finds include articles which have never been known as native to this country, and doubtless they had their origin in the orient. War weapons, copper instruments, sharp-edged and hard as steel, indicate the high state of civilization reached by these strange people. So interested have the scientists become that preparations are being made to equip the camp for extensive studies, and the force will be increased to thirty or forty persons.I am afraid that I am becoming more and more skeptical about reports of coverups and strange phenomena. The Grand Canyon is large (understatement) but it has been crawled over by hundreds of hikers, surveyors, mappers, prospectors and assorted other people for over 150 years and it would be more than remarkable if something of this magnitude had simply disappeared or covered up for all these years. As a genealogist, I picked up on the claim that the explorer, G.E. Kincaid, was supposed to be the first white child born in Idaho. If that were the case, he would have been well over 70 years old, because the first white child born in the area that is now the State of Idaho was born in 1838. See what you think. Do a Google search on Underground City in the Grand Canyon.