I grew up in Stockton, I know precisely how diverse California is.

Now I'm just plain confused -- how could somebody who grew up in the Central Valley and regularly saw trucks with confederate flags feel that Californians are some bloc that are so dissimilar from Alabamans? I'd argue that San Franciscans are way, way closer to Sydneysiders than Alabamans, but that's besides the point and misunderstands what sets the US apart from other commonwealth nations culturally. While in some ways there are huge differences, there is a common vein.

Because it has practically nothing to do with our political divide (you can find left and right anywhere in the world) and everything to do with geography and how it shapes the things we care about.

For example, find me an Alabamian who cares about how the Oroville Dam situation is resolved. Or whether California regulates housing growth at the state level instead of the city level. About how to fund or build CHSRA. Or how to preserve Sierra Nevada forests from climate change and pestilence. Or even how to build sidewalks in suburban Merced.

These things materially and significantly affect Californians, but Alabamians and Australians honestly couldn't give a fuck. But for Californians they get drowned out, both financially and in mindshare, by things that are of far less consequence. We send the majority of our taxes into to the federal ether, never to be heard from or seen again, and it should be the other way around.

Show me a government that is successful, prosperous, and popular with its people, and I'll show you one that is limited in geographic scope.

You're right about your overall point of the common vein, but your statement about Stockton seems a bit uncharitable. I lived in Stockton for 3 years and never noticed all the trucks with confederate flags. Sure, it was 20 years ago but I can't recall even one such truck.

Not in the urban centers at the bottom of the valley, but in the Sierra Nevada and its foothills. You're way less likely to encounter people like that in the Bay Area or around LA.