We have been told for yrs. like the article says, that they could only be seen from the air. I never did believe that. It appears that the oldest, were smaller, and put on mountain walls for all to see. It was a sign. Meant to be seen. I'll bet when all were built, they all had high contrast. Easily seen. Maybe even more so with a desert bloom, or a scattering of snow.
But how about this? Have you ever lived on a desert? I have no idea of the desert characteristics down there, but on the high Mojave, there are mirages year round. Maybe at times, those drawings were animated for many to witness......the desert brought them to life. BIG MAGIC.