The metal structure was first spotted on November 18 by state officials who were helping to count sheep from a helicopter, although how it got there was unclear.

Now, just as mysteriously, it has disappeared, with officials saying its removal was nothing to do with them and instead down to an "unknown party".

The Utah Bureau of Land Management said the structure, which it described as "private property", had been removed by "a person or group" on the evening of November 27.

Officials never disclosed the monolith's whereabouts but internet sleuths quickly pinpointed its location, leading to a number of intrepid sightseers making the difficult journey to see it.

The obelisk was about 3-3.7 metres high and was embedded in the red earth.

Helicopter pilot Bret Hutchings, who was among those who discovered it, said it was "about the strangest thing that I've come across out there in all my years of flying".

He told local news channel KSL TV his best guess was it had been put there by a "new wave artist" or a fan of 2001: A Space Odyssey.

Australian Associated Press