Strange Possibly Megalithic Rock in Washington State

This large stone is on my family's property in the foothills of the Olympic Mountains. The stone looks unnaturally rounded on the corners and smooth on the south facing side which may have been the "top" of the stone when it was once standing upright.

The corners align with NE, NW, SW and SE, which means the sides are aligned to the cardinal directions. The corners seem to be hewn or worked to some extent.

Was this stone altered at some point in the past to mark the cardinal directions N, S, E, W?

Another more thorough excavation may lead to further clues in the future, but for now it remains a mystery.