Petroglyphs In Utah

The pictograph drawings located in Dinosaur National Monument were probably made by the Fremont people about 1,000 years ago. Using sharp tools, they pecked away at the dark natural stain on the rock surface - called "desert varnish" to reveal the light-colored sandstone beneath.

Some of the designs, such as bighorn sheep and other animals are easily recognizable, but their meaning is not. No one knows if it was religious art, a symbolic language or simply something created.
I just cannot understand why it was necessary that they had to be painted primarily on very high cliffs AND how did they do it?

The petroglyphs were not fenced off in any way. You just were not supposed to touch the rock art.These were in a different park of the park. Notice the lizard near the bottom middle of the picture.I happened to notice these to my left when we were driving down into the canyon.