A third enigmatic metal monolith was discovered, this time atop a mountain in California, only a week after Utah and Romania found identical structures.

The monolith was spotted on Wednesday in the small town of Atascadero, in central California's San Luis Obispo County.

According to local Atascadero News, the structure is situated at the top of Pine Mountain, a local beauty spot.

Many people have already rushed to the site to see and take pictures of the enigmatic structure.

The study reported that the structure appeared to be made of stainless steel, 10-feet tall and 18 inches wide, and about 200 pounds in weight.

There is no detail on who built the structure or why, as with other monoliths sighted in recent weeks.

It comes after two more monoliths have been identified over the past few weeks.

On November 18, the first metal structure was spotted in Utah, leading to speculation about why and by whom it was built.

The pilot who first spotted the Utah structure said he thought it could be the installation of an artist, while several competing theories arose as well some eventually involving aliens.

A bureau team in Utah reported during a site visit on Saturday that the illegally built structure had been removed by an unknown individual or party.

There was so much foot traffic in the desert surrounding the statue, the crew of climbers-gone-environmental TMNT decided.

"This land was not physically prepared (especially during a pandemic) for the population shift," the group wrote in a post.

On 26 November, on Batca Doamnei Hill in northern Romania, a similar metal structure was identified, leading the local mayor to write a statement urging "those who think that there is still life in the universe" not to panic.

In California, this third monolith emerged just one day after the Romanian one vanished from the top of Batca Doamnei Hill.

Gary Lyons, who says he runs and hikes every day in the city, told Sky News that he noticed the object on Wednesday in California and that it wasn't there the day before.

The monoliths bear a similarity to a metal shape seen in 2001: A Space Odyssey by Stanley Kubrick.

In the movie, apes are seen in the desert discovering a metal monolith.

Millions of years later, on the Moon, another one was discovered.