Sachi, You need to get the layout and compass degrees and actual level measurements from center to center of each boulder, the geometry or layouts are always more important than what is on them. (for instance if it is a chain trail it will have a good Compass degree between them as well as a known turning degree to the next Boulder), if it were a triangle the distance would make sense between the legs or all of them added together. etc. Because there are two they must be a known distance apart and a compass degree for sure, assuming that they relate to Each Other.