California Penal Code 487 PC “grand theft” is a “wobbler”. This means that depending on (1) the circumstances of your case, and (2) your criminal history, the charge may be filed as either a misdemeanor or a felony. What will likely influence the prosecutor one way or another is (1) the amount of money or value of the property taken, (2) if you have prior convictions for theft related offenses, (3) how vulnerable the victim was, and (4) how sophisticated was the crime.
If you are convicted of grand theft as a misdemeanor, you face up to one year in a county jail. If you are convicted of grand theft as a felony, you face 16 months, or two or three years in state prison. However due to California’s new law AB-109, if you are convicted and sentenced to state prison for Grand Theft you will serve that time in the local county jail.