> I'm not even talking about immigration from outside the US...

Migration, or internal migration is probably a better term here.

It isn't just the migration either - it is the nature of what happens. The top cities/areas for several industries are here, and many secondary ones as well. Film production, software/web, lots of aerospace. It also helps that a fair bit basic needs are provided back to the state by itself (Central Valley farming).

The UK has drawn well educated people from the rest of the EU.

Yes, and it's the main reason our economy hasn't tanked. But there have traditionally been more barriers to movement from the EU, not least language, so the effect is somewhat less, and easy immigration from the EU hasn't been going on for nearly so long. And don't get me started on Brexit...

No it doesn't. California is 8th in terms of GDP per capita within the U.S. If you look at the list of states that are within +/- 10% of California's GDP per capita, you've New York and Massachusetts (which are suffering from out-migration), and Colorado, Nebraska, and Minnesota (none of which are major targets of internal or external immigration).

While your data are no doubt correct, this doesn't stop it being true for California. Just because a state is now suffering from out-migration doesn't indicate it didn't become wealthy from migration in the past, nor does it indicate it is getting poorer now due to that out-migration. To know that, you'd have to measure the economic contribution of the people moving in and of the people leaving. It is possible for the GDP per capita to increase and simultaneously for the population to decrease slowly.

Would be interesting to know where the wealth comes from in Colorado, Nebraska and Minnesota. I don't know enough about them to comment.

Edit: some data here: https://www.ocregister.com/2018/01/31/california-migration-c...

"The top relocation motivation for 65 percent of households arriving by van said they came to California for jobs. Only 43 percent of those departing by moving van described the move was work-related.

The jobs rush means your new neighbors are likely wealthier than the people they replaced. United’s study showed 68 percent of arriving households make $100,000 or more annually; just 63 percent of those departing by moving van make above that threshold."

OP made the assertion, they've got the burden of providing data in support of it. I'm just explaining that the data he did offer doesn't support his conclusion.

Wealth in Colorado, Minnesota, etc., comes from the same place as anywhere else. The U.S. is a rich country with lots of productive industries. Tech is actually a pretty small portion of that (5-6% of GDP, 3% of employment). E.g. Target is based in Minnesota, and has double the revenues of Facebook.

Because I can't resist: Facebook has 6x better net margin; comparing the revenues of a global retailer to those of Facebook is a bit of an odd choice.

I think it just means CA has managed to outsource more labour than the UK. Think of all the workers in China making Apple phones, or all the Uber drivers in the world forking over a chunk of their business to people in CA. It would be interesting to see the results if we could compute a per capita GDP that was actually divided among all the workers that support a given region's economy, regardless of whether they live in that region.