If the woods are troublesome for finding anything then you might need a map to find the original "map " . Then what do you do ?. If what it is supposed to be indicating is nearby you may have come across "them " earlier in which case no need for the map. If they are more distant do you then remember the info but if so pretty soon your'e back to the original problem ,in the woods not knowing where to go and in need of a map . Where you find one marked rock often enough there will be others , so you miight find another "map" which will have entirely different info from the first , i..e. a different number of markings and in a different configuration , do you then accept this one as the real " map" ? Then there is the problem of the map maker how did they know how to replicate the configuration accurately when they also had the problem of being in the woods which caused the problem in the first place ? More likely punters did know their way around to important spots in the landscape whether in trees or otherwise and had no need for maps particularly "Flintstone " style ones .