The largest triangle I have actually measured was 198 feet on the legs, but they can be bigger if they are just using them as reference points. I would look fairly close, yes the arrows should go to either markers/monuments or the spots they were marking. Since the frog looks fairly straight out, I would guess the mine, tomb, or vault was the upper arrow, and the lower arrow goes to a secondary site, possibly where things were moved and cached out. The elongated brick shaped rock is an indicator directional pointer and I've seen them next to tombstone shaped boulders laying flat on the ground pointing a direction to look from the tombstone marker.