That misdemeanor penalty is only for the first offense and with the condition that you only have one or two (max) listed firearms in your possession and you have not been convicted of the same offense already.
This portion of the section states that upon conviction you could be sentenced to State prison, which is only for felonies. You can be sentenced to County jail for either a felony or a misdemeanor up to one year for one offense. Sentences for multiple offenses can be run consectutivley, so it is possible that you could spend more than one year in County jail. So this offense looks like it is a "wobbler" and can be charges as a felony or a misdeameanor. This is up to the discretion of the D.A. that is charging the case or the judge hearing the case.
"Except as provided in Section 12288, and in subdivisions (c) and (d), any person who, within this state, possesses any assault weapon, except as provided in this chapter, is guilty of a public offense and upon conviction shall be punished by imprisonment in the state prison, or in a county jail, not exceeding one year".
In addition to all this, you will also have the firearm(s) confiscated and destroyed. If you get convicted of a felony you will lose ALL of your other guns and the ability to possess them ever again!!!!