This one is on a hiking trail at Stadium Park in Atascadero.
Naturally, the phenomenon has garnered the attention of the internet.
Some people think it's an artist, or multiple artists, creating works of public art. Others have theories that are out of this world.
More than a week after a monolith was discovered in Utah, it was taken away by a group that said they wanted to protect public lands. It's unknown who originally put it in the desert.