The San Juan county sheriff said the office did not have the resources to devote much time and energy to investigating who took the object away, which was illegal to begin with because it was placed without permission amid red rocks on a remote section of public land.
The creator of the monolith also remains a mystery. Authorities are accepting tips from anyone who saw anything suspicious related to the discovery.
The monolith was spotted on 18 November by state helicopter crews helping wildlife biologists count bighorn sheep. It was about 11ft tall and appeared to be made of stainless steel.
Utah officials did not say specifically where the monolith was located, but people soon found it through satellite images dating back to 2016 and determined its GPS coordinates.
Hundreds travelled to see the gleaming, almost otherworldly object. Visitors parked vehicles on plants and left behind waste, the federal Bureau of Land Management (BLM) said, adding that the site does not have a parking lot, bathrooms or cellphone coverage and some cars had to be towed from the remote area after getting stuck.
The site is now empty except for a piece of rectangular metal covering a hole where the monolith stood.
The BLM reminded any would-be visitors that driving off designated roads in the area remains illegal.