Stumbled upon by bighorn sheep counters, the tall metal object in the Utah desert baffled officials — and delighted the public, who began speculating on a scene straight out of a science-fiction movie.

There were theories — the work of an artist? aliens? — but no one seemed to know who put it there or why.

Now the monolith has vanished, leaving the curious with even more questions. The Utah Bureau of Land Management said this weekend that it has heard of “a person or group” removing the object on Friday night.

“We have received credible reports that the illegally installed structure, referred to as the ‘monolith’ has been removed from Bureau of Land Management (BLM) public lands by an unknown party,” the bureau said in a statement that was posted on Facebook. It added that it does not investigate “crimes involving private property” such as the monolith.

Utah Highway Patrol Cpl. Andy Battenfield confirmed to The Washington Post on Sunday that the structure is gone, but he said he could not speak to who took it or when.

So people are left to wonder.

“The space aliens returned to remove it,” one person commented on Facebook beneath the Bureau of Land Management’s update. “The structure had gathered the needed data. That’s what they told me, anyway.”

“I liked it!” another person wrote. “Maybe it will appear in another place.”

The Utah Department of Public Safety was surveying sheep by helicopter on Nov. 18 when workers discovered the monolith “installed in the ground in a remote area of red rock,” authorities said.

Pilot Bret Hutchings recounted the excitement of the find to KSL-TV.

“There’s this thing back there — we’ve got to go look at it!” Hutchings recalled a crew member saying.

“We were kind of joking around that if one of us suddenly disappears, then I guess the rest of us make a run for it,” he said.

The hunk of metal quickly generated online buzz. The New York Times investigated whether the deceased sculptor John McCracken, a science-fiction aficionado, might be responsible for it. (“His dealer says yes. His son says maybe. His artist buddies … say, no way,” the Times summarized.)

The Department of Public Safety refused to disclose the monolith’s exact location, warning that people who try to visit it might end up stranded. But some went searching anyway. The Salt Lake Tribune, which confirmed the object’s disappearance Saturday, spoke with disappointed visitors who drove hours to catch a glimpse.

All that remained Saturday, according to the Tribune: a metal triangle and a hole where the monolith used to stand, surrounded by the tracks of those who came to check it out.

Colorado resident Riccardo Marino told the newspaper that he saw a truck driving away from the area with a big rectangular object.

Then he realized the monolith was gone.

It was a “very eerie feeling, arriving in the moonlight to nothing there,” Marino told the Tribune.

Marisa Iati contributed to this report.

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