This Is Puzzling to Me

At Anza Borrego Park, there were all of these great boulders lying around. But apparently the people who lived here a few hundred years ago only used them to grind up grain. Here's one of the morteros (mortars) they used by my shoe. And look at the great boulders they left alone.

 

 

 

 

 

 

 

 

 

 

 

They did have time to do some painting. Here I am wondering if there is still some room on the rock to spray paint a greeting.