Cairns are rock formations in which rocks are stacked on top of one another. Yosemite National Park made a controversial media post in July by asking visitors to knock them down to combat the anti-leave-no-trace art projects.

However, officials at Joshua Tree, Death Valley, Canyonlands and Arches national parks disagree.

“Cairns are a nuanced topic,” Death Valley spokesperson Abby Wines told SFGATE in a statement.

While some of the cairns that mark hiking trails and routes are done by park rangers, most are created “by hikers trying to pay it forward to help other hikers,” Wines told SFGATE. “These cairns are useful and should be left where they are.”

She also said that sometimes cairns are used to mark historic features.

“Cairns were used to mark boundaries of mining claims and land survey points in this area in the late 1800s and early 1900s,” she said. “Now these are helpful for historical archaeologists and should be left in place, just like historic trash around old mining camps should be left in place.” 

Wines said that guests should never build cairns but also should avoid knocking them down.

“It’s like graffiti, but fortunately, easier to clean up!” Wines said. “I wouldn’t recommend that most people dismantle cairns because sometimes only the park rangers have enough context and information to know whether a cairn is a trail marker, a historic feature or vandalism.”

A spokesperson for Yosemite National Park did not respond to a request for comment. 

Karen Garthwait, spokesperson for Utah’s Arches and Canyonlands national parks, had a similar position. She explained that rangers sometimes build rock cairns that vary in size and appearance.

“Appropriately sized rocks are not uniformly distributed on all trails, and some trails require taller cairns if the desert terrain is uneven/has challenging sight lines,” Garthwait told SFGATE in a statement. “That said, ranger-built cairns tend to have at least three levels of rocks, are built for stability, and are positioned so that you can see the next one at a linear distance from the previous one. Rock stacks that are grouped together like a sculpture garden or contain any vertically balanced rocks that look precarious are more likely to be visitor-built sculptures.”

However, visitors sometimes create unwelcome cairns next to an official one, so Garthwait said that notifying a ranger is a better approach. 

Although Joshua Tree rangers do not use cairns at all, Joshua Tree spokesperson Hannah Schwalbe said a few unmaintained routes in the park have cairns along them created by visitors; however, “they should not be relied solely on for navigation,” she said. Visitors can better follow “leave no trace” practices by not interacting with the rocks at all. 

“If there are confusing cairns along maintained or unmaintained trails or routes, visitors should report those to a ranger. Park rangers will go out and dismantle any confusing, unnecessary or eyesore cairns along maintained trails,” Schwalbe told SFGATE in a statement.

She suggested that visitors plan and prepare for each national park before arriving to remain aware of their individual policies.

“There is no one size fits all for national parks, and it’s important to follow the rules when you are visiting a new [protected] place,” Schwalbe said. “National parks protect a huge range of ecosystems and landscapes, and different management techniques are required to best manage each of those diverse places!”