Petroglyphs in the Valley of Fire

Within the canyons of the Valley of Fire. 

These were my main reason for visiting the Valley of Fire Henry,

I wanted to see the petroglyphs.

I had read in Guns, Germs, and Steel about the lack of a written language in native US cultures...but couldn't these and other imagery (e.g. hide painting) be indicative of a written language?

I need to write to Jared Diamond and find out.

xoxo a.d.