Rock Cairns

Have you ever come across strange stacks of rocks while hiking in national parks? Maybe you wondered what they are and if they mean anything. Wonder no more—these rock piles are called cairns and often mark hiking routes in parks. Every park has different rules about cairns, so it’s always a good idea to check out a park’s website for information on hiking trails before you go.

The rock cairns at national parks like El Malpais, Hawaii Volcanoes, and Acadia are carefully maintained by park staff to keep hikers like you on the correct path. The cairns at Acadia National Park in Maine not only guide visitors, but also add some historical interest to the hiking trails. In 1896 Waldron Bates, lead author of the hiking map still referenced to create today’s trail maps of Acadia, developed a standard for building cairns in a unique style we now call the Bates cairn. However, starting in the 1950s or 60s the Bates cairns were replaced by the traditional conical cairns. Then, in the 1990s, Acadia National Park began recovering this little piece of history by re-establishing and building Bates cairns on the many east-side trails in the park. If you’re unsure about following cairns on your hike, ask a returning hiker or any park ranger.
two large rock columns with a long horizontal rock placed atop the two columns and a sunset behind it
A Bates cairn at Acadia National Park

Image Courtesy of Brandon Hoogerhyde

Other parks don’t build or maintain rock cairns and warn visitors to not rely on these rock piles to guide their hike. Any rock cairns are ornamental and can often become a problem for hikers who think they are supposed to follow them. Before visiting a park check out their website for information on their hiking trails and signage.
small stack of red rocks in a conical shape on top of a boulder
Small navigational rock cairn at Canyonlands National Park. Trails at Canyonlands are usually marked with cairns and have signs at intersections. Many remote trails do not receive regular maintenance and may not be adequately marked. All backcountry hikers should carry a topographic map

NPS/ Neal Herbert

Each park has a different way it maintains trails and cairns; however, they all have the same rule: If you come across a cairn, do not disturb it. Don’t knock it down or add to it. Follow the guidelines from the Leave No Trace Center for Outdoor Ethics to ensure future hikers can navigate the trail and prevent damage to the landscape:
  • Do not tamper with cairns – If an intentional cairn is tampered with or an unauthorized one is built, then future visitors may become disoriented or even lost.
  • Do not build unauthorized cairns – Moving rocks disturbs the soil and makes the area more prone to erosion. Disturbing rocks also disturbs fragile vegetation and micro ecosystems.
  • Do not add to existing cairns – Authorized cairns are carefully designed. Adding to the pile can actually cause them to collapse. Now that you know a little bit about cairns, check out these examples that you may come across on your next hike.
Now that you know a little about cairns, check out these examples that you may come across on your next hike.
small conical rock pile on the dirt trail
Navigational rock cairn at Zion National Park

NPS/Caitlin Ceci

large stack of gray rocks in a cone shape on a lava field
Large ahu or rock cairn at Hawai'i Volcanoes National Park.
You can see why it's important for visitors NOT to stack rocks in national parks. These rock cairns are maintained by park rangers to mark trails. In areas like the East Rift Zone, where it is easy to become lost, the ahu are welcome sights for hikers.


Last updated: November 27, 2023