Russell’s Cairn at Windy Gyle is supposed to mark the site of the mysterious death of Lord Francis Russell in 1585. He was in a truce meeting with the Scottish Warden Thomas Ker at the time. It’s thought that he could have been bumped off as part of an English plot to remove Ker and other Catholic supporters of Queen Mary from their positions of power by implying they murdered him. The cairn’s thought to be Bronze Age though, and there are others along the ridge.
See:
archive.org/stream/uppercoquetdalen00dixo#page/51/mode/1up