Because the structure is built on "glacial till" that consists mainly of large, random-sizedrocks and boulders, it proved impractical to dig holes deep enough for directly setting the posts without either hitting large rocks or totally digging them out, which would produce a very wide hole requiring extensive back filling. Consequently, single concrete piers, set 2-4' deep, often atop rocks, were used as supports for each corner.
Eight piers are ready for a conventional deck. Why eight? After four were poured, the location had to be shifted 5' back, away from a large, leaning tree trunk, which would have come within 8" of the roof overhang (and probably grazed during a hurricane). Two extra piers now support the center of the azumaya while the farthest pair supports the projecting entry deck, which was the consequential afterthought of this last minute change.