I was wondering the same thing.
Also, that does not look like basalt. Our area in North Idaho and northeastern Washington is covered in a mile-thick layer of basalt. It’s a hard, dark gray-black igneous rock. It is extremely hard, too.
Here exposed basalt has (I guess) a higher iron content, exposed Cretaceous era basalt is rust colored.
Even given that, if you chiseled letters into it they would probably show the unoxidized basalt color.