I get the feeling it’s related to hydrocarbons

[goldog]

Any ideas on this one. It seems to have some petroglyphs

 

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[IAMZIM]

I see you hail from the California area, you might want to try posting this in the artifacts forum.

 

[Bajahunter]

Those look like they are covered in the writing of the Havasupais, the Native American tribe that lives in the Grand Canyon.
Yours looks like it comes from a Native American tribe from the San Francisco area called the hippais

 

[goldog]

Possibly but most likely Chumash or Morango.

 

[Capt Nemo]

Might be from a tribe of Railians. They cover the yard in their petroglyphs overnight. The Rapo-po tribe is in a constant battle with them for infringing on tribal lands and defacing their religious artifacts.