The nearly 12-foot high smooth metal structure was found on public land while Utah state employees were counting bighorn sheep by helicopter.

The monolith appeared in the red-rock area south of Moab sometime between August 2015 and October 2016, according to Google Earth's historical view.

The US government said the Utah monolith was reported missing on Friday. That same day, Romanian media reported the discovery of a similar structure.

In the last two weeks, three metal monoliths have appeared across the world: one in Utah, one in Romania, and now another in California.

Aliens could see Earth passing in front of the sun and notice the chemical footprints of life in our atmosphere.

Jupiter bombards Europa's surface with radiation. The resulting "mosaic" of glowing ice could hint at the potential for life in the ocean below.

With the latest monolith appearance in California, here's a timeline of the structures appearing and disappearing in Utah, Romania, and California.