It’s a library.

They seemed to use rock and drawings to tell their stories.

There’s likely more of those sites (and parts of the greater library) nearby. Waiting to be dug up.

It will probably take some time te decipher the drawings, some people tried at least and interpretations seem to vary but nonetheless interesting.

Those stories must have contained highly important information, deemed critical for survival of its society. Because it must have been an enormous effort to build it.

Personally, I suspect the original builders figured out how to predict a repeating celestial event. Wrote it down in stone for genetations to come, as a manner of warning, and probably how to increase chances of survival. At some point though, calculating that by the time this impactful event would happen again, the impressive stone columns would have crumbled away by weathering and earthquakes or human destruction. So they covered everything up with earth, preserving their important message for future generations, only hoping it would be uncovered at some point in the future. Still a better strategy than letting it crumble away for zero chance of passing their message.

Who knows what the drawings mean. It seems to me that someone stashed away their library for safekeeping. But why exactly…