California taxes non-residents on CA-source income. A capital gain from the sale of real estate located in CA is CA-source income. CA does not have a separate capital gains rate. A capital gain is taxed as ordinary income at a rate determined by the amount of the gain and the taxpayer's filing status. You can find CA's tax rate schedule here: https://www.ftb.ca.gov/file/personal/tax-calculator-tables-rates.asp
**Answers are correct to the best of my ability but do not constitute tax or legal advice.
