Corrections officials said the episode at Calipatria State Prison began in the exercise yard about 6:30 p.m. Saturday when the one inmate began stabbing the others with a homemade weapon. The group got him to the ground and started beating him.
Ultimately about 115 prisoners were involved, the Los Angeles Times reported. Guards fired a warning shot with a rifle, and then used foam-tipped bullets and pepper spray to get the inmates back under control, the newspaper said.
Nine inmates were taken to area hospitals with "moderate to serious injuries," a Corrections Department statement said. No staff was hurt.
A second disturbance started later in a dining facility and kitchen, and lasted about 7 minutes.
Prison officials said the facility, located in Imperial County and home to 3,500 inmates, was placed on a "modified program" that limits inmate movement while the riot is investigated.
About 1,700 of the prisoners are serving life sentences, including nearly 600 who have no chance of parole.
LGBT community has 'bullied the American people': Bachmann
Duggar sisters unveil Christian dating rules in new book