Please clarify: Was it your California tax return that was not accepted or your federal tax return (1040)?
The IRS is federal. California is the FTB Franchise Tax Board. Does the letter say you did not file or did not Pay the tax due?
Did you efile? Was it Accepted? Maybe you didn't finish filing it or it Rejected. When you log into your account you should also see the status and if it was Accepted or Rejected, Started, Printed, Ready to Mail, etc. what does it say?
Then when you efile you get back 2 emails. The first email only confirms the transmission. The second email says if the IRS (or state) Accepte.d or Rejected your efile. Check back though your emails if you have them.
In the PDF of your TurboTax return, the last page of the federal return should be an "electronic postmark" that shows your name, Social Security number, the date and time that you e-filed the return, and the date that the IRS accepted it.
How to access prior online returns