Please Help Identify Bizarro Rock Marks

[PaleoAnything]

Found on beach on California's Central Coast. I'm baffled as to what may have caused these indentions. My present theory is that while this rock was forming, the material was up against ... something. Listen: I'm just throwing stuff at the wall here -- I have NO idea, lol. Do you?

 

[Tigger]

Pix of sides please?

 

[Mrdigz]

Kind of hard with these 2 pictures. Pat a couple more of possible.