UPDATE: Dec. 1, 2020, 12:48 p.m. EST Looks like otherworldly creatures didn't take the monolith back to their home planet. Rather, some fed-up locals seem to be behind the heist. Here's more on who may be behind the mysterious removal.

The metal monolith, planted by unknown sources in the Utah desert at some point before last week, has gone the same way it arrived: shrouded in mystery.

Officials from the Utah Department of Public Safety and the Utah Division of Wildlife Resources discovered the three-sided silver structure on Nov. 18 via helicopter, while on a routine mission to count bighorn sheep.

Now the monolith is no longer — except for some remaining rocks and a triangular piece of metal, according to visitors who posted photographs online Saturday.

Prime Day deals you can shop right now

• iRobot Roomba Essential Vac Q011 Robot Vacuum Cleaner—$159.99(List Price $249.99)

• Samsung Galaxy Tab A9+ 10.9" 64GB Wi-Fi Tablet—$142.49(List Price $219.99)

• Apple AirPods Pro 2nd Gen With MagSafe USB-C Charging Case—$168.99(List Price $249.00)

• Fitbit Charge 6 Fitness Tracker With 6-Months Membership—$99.95(List Price $159.95)

• Apple Watch Series 9 (GPS, 41mm, Midnight, S/M, Sports Band)—$279.99(List Price $399.00)

Tweet may have been deleted

Tweet may have been deleted

With no clear explanation for the disappearance in sight, Twitter users began speculating on the latest strange twist in a very strange year.

Tweet may have been deleted

Tweet may have been deleted

Tweet may have been deleted

Tweet may have been deleted

One leading theory is that the monolith was the work of a California artist who died in 2011 — and was a friend of Star Trek actor Leonard Nimoy. In its sudden disappearance, however, some detected the hand of another more prank-friendly artist.

Tweet may have been deleted

So far as we know, there was no attempt to vandalize the monolith — though it seems like the kind of thing humanity would do to its first alien visitor.

Tweet may have been deleted

With no leads in the case, local authorities — specifically, the Sheriff's Office in San Juan County, Utah — declined to investigate. But they did decide to have some fun on Facebook.

Wherever the monolith dwells now, it's clear that 2020 isn't done with its surprises. Perhaps we shall see this modern version of the crop circle again before the year is out.

Related Video: College students discovered an invisible ancient text with their school assignment