Mounds of stone built up during ancient lead mining operations in the Yorkshire Dales are under threat, a study shows.
The 200-year-old spoil heaps are themselves being mined for aggregate to upgrade tracks, the Yorkshire Dales National Park Authority said.
It is urging landowners to help preserve the heaps, which contain vital information about the mining industry and Dales geology.
Experts warn that uncontrolled removal could result in the heaps disappearing.
Large areas of lead mining remain, particularly in Wensleydale, Swaledale and Arkengarthdale, and are designated as Sites of Special Scientific Interest (SSSI).
Robert White, the authority's senior historic environment officer, said: "The National Park is scattered with the remains of former mineral extraction and processing sites, especially lead industry remains, most of which date from the 18th and 19th centuries.
"The reuse of former lead mining waste as aggregate happens frequently on shooting estates, but mine spoil is a finite and diminishing resource and the considerable loss of it in recent years raises both conservation and environmental issues.
"Uncontrolled removal is severely damaging the historic integrity of largely unrecorded lead mining landscapes."
He said the waste material allowed archaeologists to analyse the minerals, periods of activity and dressing processes involved after the underground rock was brought to the surface.
Many spoil heaps contained tools and other artefacts, while others covered the evidence of earlier phases of mining activity.