If I withdraw money from an old 401k account in FL, how much will I be taxed in CA and federally?

You have not mentioned your age.   If you are younger than 59 1/2 you will pay a 10% early withdrawal penalty to the feds, plus be taxed at your normal tax rate.   CA will also tax you at your normal tax rate.  The fact that the fund originated in FL has no relevance.  We cannot predict "how much" you will pay in tax since we have no amounts to go on and no information about your other income.

You will receive a 1099R for the distribution which you will enter when you prepare your federal return.  The information will flow to the state return.

To enter your retirement income, Go to  Federal> Wages and Income>Retirement Plans and Social Security>IRA  401 k) Pension Plan Withdrawals to enter your 1099R.

@kgarson85 you will pay whatever your federal and state tax bracket is times PLUS the 10% penalty times the $21k.  it is very expensive - Congress really wants you to leave the money in the 401K until retirement. 

if you are in the 12% federal tax bracket and the 6% CA tax bracket, you would pay 28% times $21k. Again, quite expensive.