I had a similar question, and found this in State of California Franchise Tax Board publication FTB-1031, "2018 Guidelines for Determining Resident Status". On page 8, under IRA distributions, it states:
"IRA, Roth IRA, SIMPLE IRA, SEP, and Keogh distributions received after becoming a nonresident are not taxable by California if received after December 31, 1995."
To me, it's clear that once you become a nonresident, or you've always been a nonresident, the distributions you receive are not taxable by California.
