I have trees like these near rivers. They didn't need to mark water this way. They are along trails, some very old trails. Anybody can find water when it is flowing in the canyons a few hundred feet away. The water theory on markers has always been hilarious to me and my friends. The same type markers people have been posting here for years that claim water marker, we have seen within a few hundred feet of a river that is massive, like you would have trouble swimming across. Perhaps these old explorers were totally blind. Also I have heard the markers being for old livestock trails.... makes sense , yeah right lol . Move a 10 -80 ton boulder with horses so you can know where to funnel your livestock. The boulders were placed there long before...
BTW did you notice how clear the area is around those tree markers so they stand out so well? They stick out like a sore thumb.