Days after the discovery and swift disappearance of two shining metal monoliths spotted half a world away from each other, another towering structure has popped up – this time at the pinnacle of a trail in Southern California.

Its straight sides and height appear similar to one discovered in the Utah desert and another that was found in Romania.

Like those structures, the origins of the California edifice are also mysterious.

It is at the top of a hill in Atascadero, about halfway between San Francisco and Los Angeles, Keyt-TV reported Wednesday.

The tall, silver structure drew hikers to the area after photos were posted on social media.

A similar one spotted about two weeks ago in Utah’s otherworldly red-rock country became a beacon of fascination around the world as it evoked the movie “2001: A Space Odyssey”, and drew hundreds of people to the remote spot.

Romania US Metal Monolith
A metal structure sticks from the ground on the Batca Doamnei hill, outside Piatra Neamt, northern Romania (Robert Iosub/AP)

But it soon disappeared, as did a similar structure that appeared last week in Romania.

Whitney Tassie, a curator of modern and contemporary art at the Utah Museum of Fine Art, said the monolith was fascinating in part because of its context in the landscape.

“That’s a big, big part of land art in general is this idea of an experience, of a journey,” she said.

The intense social media reaction to the monolith against the backdrop of a punishing pandemic, along with the quick destruction of the piece, has become a part of its story, she said.

“It’s good to think about our relationship with the earth, which is ultimately what these sorts of projects do,” Ms Tassie said.

“Man’s impact on the environment front and centre.”

Two extreme-sports athletes said this week that they were part of a group that tore down the monolith in Utah because they were worried about the damage the droves of visitors were causing to the relatively untouched spot.

Officials said the visitors flattened plants with their cars and left behind human waste.