Last updated: December 30, 2024
Article
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 they are often used to mark hiking routes in parks. You should leave them as you find them, as they may serve an important purpose.
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.
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.

Image Courtesy of Brandon Hoogerhyde

NPS/ Neal Herbert
- 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.

NPS/Caitlin Ceci

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.
NPS