The park posted a video on Facebook earlier this month instructing visitors to stop building large rock towers, called cairns, and dismantle any they find. In the video, a wilderness restoration ranger gently shoves over a cairn, which appears to be several feet high.

“This dramatically oversized cairn is a mark of human impact and is distracting in a wilderness setting,” the post read. “Building rock cairns also disturbs small insects, reptiles, and microorganisms that call the underside home!”

Constructing such towers goes against Leave No Trace ethics, a set of seven principles designed to educate members of the public on minimizing their impact on outdoor spaces and that the National Park Service advises its visitors to follow.

According to the park service, cairns are most commonly used to designate hiking routes. Typically cairns should be assembled only by rangers and trail workers, according to the park service.

“When used appropriately, rock cairns are great for navigation, safety, and delineating a new or hard-to-follow trail,” Yosemite said on its Facebook post.

The spring and summer months are peak seasons for the National Park Service system, with flocks of tourists packing parks across the country.

The park service did not immediately respond to requests for comment.