...and I put my new found knowledge to (not so) good use: there is a fine set of petroglyphs that I made under a sandstone overhang near (but not too near) a SoCal nature trail.
So far, I'm still waiting to hear that they have been "discovered".
:’) I hope you get a chance to photograph them in detail, before someone else “discovers” them and screws them up with their own idea of writing, or tries to cut them out to sell or whatnot. :’)