Fourteen parks along the west coast, plus three you need a plane and an ocean to reach.
The mainland eleven make obvious sense: the Sierra Nevada, the Cascades, the redwoods, the Olympic Peninsula. Coast, volcano and big-tree country, all on one north-south corridor.
Then there is Hawaiʻi, and then there is American Samoa, which is 2,600 miles past Hawaiʻi and the only US national park south of the equator. It is also, at around 43,000 visits, one of the least visited parks in the system, and getting there is a genuine expedition.
Calling American Samoa "Pacific" is true in the ocean sense and useless in the road-trip sense. We kept it here because the alternative was a region of one. If you are working toward all 63, this is the park to plan around first, not last.