Sorry to bump this thread, but I'm in the same situation: did not set foot in CA in 2017 (previously lived there but moved away in 2015), but received contracting income reported on a 1099-MISC from a California-based company. The advice given in this thread -- that the income is not "California source income" and therefore not taxable by California -- seems to contradict lots of information I can find elsewhere. And apparently this may have changed very recently. In May 2019, the California Office of Tax Appeals ruled very recently that income from California-based clients is taxable as California source income.
For some discussion:
https://www.coblentzlaw.com/california-office-of-tax-appeals-gives-precedential-authority-to-bindley...
https://money.stackexchange.com/questions/95243/is-self-employed-work-performed-out-of-state-for-a-c...
