After you file

I believe you are dead wrong. 

Here is the link from the CA FTB:

https://www.ftb.ca.gov/tax-pros/efile/efile-for-individuals.html

It says "

You can use e-file for these types of California tax returns:

• Original returns (this tax year and past two years)
• Amended returns (this tax year and past two years)"

Here is the link in turbotax that says how to do it:

https://ttlc.intuit.com/turbotax-support/en-us/help-article/tax-return/amend-california-state-return...