Rangers at Yosemite National Park have asked hikers not to stack up rocks to create their own cairns, and to dismantle ones made by other park visitors. The National Park Service (NPS) posted the request on Facebook, together with a video of a ranger kicking over a particularly outsized cairn built by members of the public.
"According to Leave No Trace ethics when we recreate in wilderness spaces, our goal is to leave no signs of our impact on the land and respect other creatures living in it," the NPS wrote.
"Unfortunately, this dramatically oversized cairn is a mark of human impact and is distracting in a wilderness setting. Building rock cairns also disturbs small insects, reptiles, and microorganisms that call the underside home!"
This particular cairn was so tall that it could also have posed a serious danger to children or animals if it collapsed.
The NPS agrees that rock cairns have a purpose, and can be useful for navigation, safety, and delineating a new or hard to follow trail, but says they should generally only be built by Park Rangers and trail workers.
Knock it off, and knock it down
DIY cairns aren't just a problem in the US. Last summer, Park Rangers in Australia issued an almost identical plea, asking people to stop piling up rocks in Cania Gorge National Park. The complaint came after Ranger Cathy Gatley came across a creek bed where every single rock had been stacked.
Removing the stones can accelerate erosion of riverbeds and lead to flooding further downstream, among other issues.
"The rocks help to absorb water, and they prevent runoff," Gatley told ABC News at the time. She added that they also provide a habitat and refuge for plants and animals, and moving them leaves creatures without a place to shelter, or to hide from predators.
