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If you move from California to another country, and are subject to US Federal Income tax, and don't qualify for an exemption, the Franchise Tax Board still considers you a resident of the state, and as such, taxes you on your worldwide income; as you did not end your residency by establishing residency in another state.While this is strictly correct, I think the implications of what you wrote are too strong. If you move from California to another country or U.S. state, the requirements to get an "exemption" from California tax residency are essentially "convince the FTB that you have weaker ties to California than to your new location."
While arbitrary and open to abuse in theory, it appears less so in practice. Quoting from California's Guidelines For Determining [Tax] Resident Status [1], heading "Leaving California" on page 6:
> Example 4 - You and your spouse/RDP are California
residents. You accept a contract to work in South America
for 16 months. You lease an apartment near the job site.
Your contract states that your employer will arrange your
return back to California when your contract expires. Your
spouse/RDP and your children will remain in California
residing in the home you own.
> Determination: You maintain strong ties with California
because your spouse/RDP and children remain in your
California home during your absence. Your intent is to
return to California, and your absence is temporary and
transitory. You remain a California resident during your
absence. You are taxed on income from all sources,
including income earned in South America.
> Example 5 - You receive and accept a permanent job
offer in Spain. You and your spouse/RDP sell your home
in California, pack all of your possessions and move to
Spain on May 5, 2019, with your children. You lease an
apartment and enroll your children in school in Spain. You
obtain a driver’s license from Spain and make numerous
social connections in your new home. You have no
intention of returning to California.
> Determination: You are a part-year resident. Through
May 4, 2019, you were a California resident. On
May 5, 2019, you became a nonresident. All your income
while you were a resident is taxable by California. While
you are a nonresident, only income from California
sources is taxable by California.
> Example 6 - You are a resident of California. You accept
a 15-month assignment in Saudi Arabia. You put your
personal belongings, including your automobile, in
storage in California. You have a California driver’s license
and are registered to vote in California. You maintain
bank accounts in California. In Saudi Arabia, you stay
in a compound provided for you by your employer, and
the only ties you establish there are connected to your
employment. Upon completion of your assignment, you
will return to California.
> Determination: You have maintained greater connections
with California than you have established in Saudi
Arabia. Your absence is for a temporary or transitory
purpose. Therefore, you remain a California resident.
As a California resident, your income from all sources
is taxable by California, including the income that you
earned from your assignment in Saudi Arabia.
Example 5 above is closest to what I think you were talking about by "moving from California to another country." The only way I think FTB could go after you for here is to argue that you could have an "intention" of returning to California eventually, and I do not know whether keeping your American bank accounts at California banks would be enough of a hook for FTB to decide it's worth the effort to try that argument.
For myself, if I did move from California to become an indefinite expat, I wouldn't worry too much about the FTB going after me. Opinions may vary, of course.
[1] CA FTB Publication 1031, 2019 edition: https://www.ftb.ca.gov/forms/2019/2019-1031-publication.pdf