"A little heap of stones" - another mention by Ernest Seton Thompson

Thompson also says this on pp 165,166 "The Big Book of Country Living"
"Another Indian sign was a little heap of stones, meaning "We camped here because one of us was sick." This originated in the hot stones used for making steam in the vapor bath that is so much favored by the Indian doctors."

Please bear in mind that this is only one documented function of rock piles and is very unlikely to apply to places where there are numerous structured piles. But it does apply sometimes so it is worth looking for rock piles made entirely from burnt rocks.