Now you see it, now you don't: Mysterious Utah monolith vanishes into thin air

A metal monolith that appeared in the heart of Utah's Red Rock Desert over a week ago has gone.

The disappearance of the structure was as unexplained as its arrival in the first place.

According to Utah's Bureau of Land Management, the object - which has baffled Americans and triggered fevered speculation about extraterrestrial visitors - was removed on Friday evening.

The organisation said it was not responsible for the monolith's removal, which had been illegally installed in the first place.

"We do not investigate crimes involving private property which are handled by the local sheriff’s office," it said in a statement.

“IT’S GONE!” the state's Department of Public Safety said on Instagram. Almost as quickly as it appeared it has now disappeared."

The department mused that perhaps the aliens who placed the 3- to 4-metre high structure in the first place had reclaimed it.

Installing the structure, which was spotted by a biologist conducting an aerial survey of southern Utah's bighorn sheep population, would have required some work.

It was not merely dropped in place, but firmly planted into the ground, likely requiring whoever was responsible to haul digging equipment to a remote part of the Utah desert.

The authorities had tried to keep the location of the monolith secret to avoid sightseers flocking to the remote location and getting stranded.

Nevertheless, intrepid individuals did track it down near Moab, a popular tourist destination.

One of them, David Surber, mused on Instagram. "Apparently the monolith is gone. Nature returned back to her natural state I suppose.”