In case you were wondering. We've seen these "art installations" all over the parks we visit. And while every once in a while one seems slightly charming, the absolute epidemic of stacked rocks all over the place has quickly become a real eyesore.
When we were hiking on our recent trip to the Southwest, we noted this very clear sign that made it apparent: stacked rocks are graffiti. This is especially important in the Southwest, where geoglyphs and other rock installations can be thousands of years old, and indicate real archeological importance. Scrawling all over that with your own clever creations is graffiti, nothing more or less. Here's the sign: