Arches Nat. park in Utah is one of my favorite places.
The arches there do not have the square/sharp edges that this arch has. Are the mechanisms that formed this arch somehow different?
Good question; can't answer it authoritatively. I would *guess* that the age of the structures and the composition are the main determinants of the morphology. I.e., sandstone probably erodes faster and gets "rounded" more than harder rock. Sharp edges are also indicative of how the rock fractures (cleavage) -- most sandstones don't fracture sharply.