A State Penitentiary is a prison in the United States in which the state is responsible for the care, confinement, and rehabilitation of its inmates, as opposed to County Penitentiaries, which are overseen by individual counties in a state, or Federal Penitentiaries, which are overseen by the United States federal government.
California has 34 state penitentiaries, including Folsom Prison, where Joey Baines was incarcerated. In the timeline where all lawyers were abolished in the United States by the 21st century, Baines was still incarcerated at Folsom in 2015, having been denied parole twelve consecutive times.
On October 22, 2015, Marty McFly, Jr. was tried in a data-court, convicted, and sentenced to fifteen years in an unnamed California state penitentiary after being found guilty for the Hill Valley Payroll Substation robbery, which was actually masterminded by Griff Tannen. The following week, his sister Marlene was sentenced to twenty years in the penitentiary for attempting to break Marty Jr. out of jail.
These events were averted when Doc Brown picked up Marty McFly in 1985 and brought him to 2015. Marty McFly posed as his son, and told Griff that he wasn't going to participate in the theft. This led to a hoverboard chase between Marty and Griff's gang. After Marty jumped into a lake in Courthouse Square, Griff and his gang crashed into the Courthouse Mall and were jailed, thus preventing the forthcoming robbery.
- Back to the Future Part II (Mentioned only)