I'm Norwegian, I used to live in Oslo, now live in London and was considering moving to California.
The tax difference is much lower than Norwegians like to think (what would Norwegians do if there was no excuse for complaining about high taxes). I calculated my Norwegian tax, UK tax and what I'd pay in California including VAT / sales tax, and while Norway came up on top, on my - way above average salary - total tax came out at about 39% for Oslo, and about 34% for California, and about 36% or so in the UK, before taking into consideration things like difference in health care coverage.
There are places in the US where the tax gap compared to Norway is large, but California isn't it.
It's hard to end up paying around 50% tax in Norway even including what you pay in VAT, unless you make a huge multiple of average salaries. You could of course add in employers payroll taxes ("arbeidsgiveravgift"; but in that case, don't forget to do that for California as well), but if so, you're considering it part of your income and need to adjust gross salary up accordingly too - I see people try to add in payroll taxes to inflate the tax number, but nobody takes the payroll taxes into consideration when comparing salaries, or when negotiating them.
The marginal income tax band is capped below 50% (when you add in state income tax, federal income tax and local taxes, the marginal tax rates in some US locations is not that far away either), and unless your salary is way above average and you spend it all, even with the 25% VAT adds up to much less because most people simply don't spend that much of their salary on buying top rated goods. On top of that, deductions reduce the gap. Of course if you live in the cheapest place possible and spend all your remaining money on highly taxed goods like alcohol and cigarettes and warm your house with petroleum, then, yes, you may manage to end up paying 50% or more to the government.
That said, overall you'd probably come out better in SF on the same salary due to the cost of goods and services. But the "we pay so much tax" thing from fellow Norwegians is a pet peeve of mine, after I moved to the UK, and, surprise, didn't actually pay much less tax.