Some formations (Surprise Canyon, Temple Butte) are not included because they do not have sufficiently widespread outcrops. Some formations are also included as groups instead of individual formations. This is done based on what is commonly portrayed in public-facing stratigraphic columns, such as the one in the above source link or on the Grand Canyon National Park website. The basement rocks (as always) are difficult in a strat column for large areas, but there's a lot accepted for both items.
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