Walkers taking on the Yorkshire Three Peaks Challenge are being reminded not to remove rocks from drystone walls and hillsides to spell out their names for selfies.
Some people are even attempting to make their own cairns, said the Yorkshire Dales National Park Authority.
Tens of thousands tackle Yorkshire's highest peaks - Pen-y-ghent, Ingleborough and Whernside - each year.
Managers have asked visitors to respect the area.
The authority said the rearranging of stones is a "significant threat" to the national park, and suggested people do not realise that the stones they are using may come from monuments that are thousands of years old.
Kate Hilditch, area manager for the Southern Dales, said despite its rugged appearance the Three Peaks route comprises "very fragile environments" that need to be protected.
She urged people to abide by the Yorkshire Three Peaks code of conduct.
"At the heart of the code of conduct is our message to everyone to respect the land, respect the local communities - particularly the community in and around Horton-in-Ribblesdale - and to respect each other," said Ms Hilditch.
Ms Hilditch said the Three Peaks route is one of the greatest achievements to date of the Yorkshire Dales National Park Authority and its partners.
In the 1980s, the paths in many places were impossible to use, such was the scale of the erosion and bogginess, she added.