Asklemmy

You're not going to get quality answers here but it might get you started. You will get broad strokes that obscure a lot of difference. If you want to go deeper there are many directions to go in. For example you will want to think about whose perspective you're looking at cultural regions from, because the subsection of the American population you're talking about matters due to segregation, different migration patterns, etc. If you are talking very mainstream dominant culture then I would personally look up US historical trends of waves of colonialism spreading West and events like the Trail of Tears, Louisiana Purchase, Spanish-American War, amongst others that were really big in the establishment of cultural differences. A good chunk of the different cultural regions correspond to bioregions and the culture of the people who were genocided so settlers could take their land. The grease trail is a good marker for cascadia as a cultural region IMO. But the white supremacist settler idea of the "american redoubt" roughly tracks the same region. Cultural regions in the USA are subject to cultural imaginings, it's a lot less regulated than in Europe with your DOCs.

The density of different cultural regions varies by region with population density and degree of diverse migration. For example, the diner culture of New Jersey is something unique in itself, or so I hear. You get wacky foods like skyline chili or the pizza of Altoona, PA or architecural flourishes like the free-standing basement toilets of Pittsburgh. Random ass cities will have their own long standing cultural thing in the states "back east" where the majority of settler Americans live. Whereas the state of Oregon is the size of the UK & contains maybe three cultural regions if you include the state of Jefferson which is kind of just neoconfederate crankery.

But basically I think the whole question you're asking can't be summed up quickly and understanding it requires understanding a lot of history, geography, and politics to get why this country is as fucked and fabulous as it is. Like I could rattle off a TLDR of stereotypes of regions like the rainy PNW, polluted and expensive California, the snowy Rockies, the sunny Southwest, the corn covered flat Plains, the behemoth Texas. The "midwest" is somewhere between the plains and the Great Lakes Region, which bleeds into mid-atlantic to the east and new England to the NE & the South to the SE. On the eastern seaboard you got new England, mid atlantic/DelMarVa, then the South then Florida which is its own beast but also contains multiple regions. But even this is oversimplifying leaving out regions like the Big Thicket between Texas and Arkansas and Appalachia, which stretches between multiple regions as defined by states but is definitely its own cultural region, as is Acadia.

TL;DR: tough question, maybe not the right one, depends on who you ask.