More violence broke out Thursday at the California Men's Colony in San Luis Obispo.
Prison officials say it happened just after 1 p.m. at a medium custody yard.
Approximately 50 inmates were involved.
Prison officials say a group of 35 inmates rushed a group of 15 inmates.
Correctional officers reportedly ordered the inmates to stop fighting, and when they didn't comply, observation tower officers fired two warning shots. Officials say other officers used light/sound diversionary devices and non-lethal projectiles to stop the fighting.
No staff were injured but two inmates were taken to the hospital for treatment of non-life threatening injuries. Officials say one of the inmates was struck in the head and lost consciousness.
It follows a riot that occurred in the same medium custody yard on Wednesday.
CMC officials say in that incident, a group of 20 inmates rushed a group of 10 inmates and another group of 10 inmates joined in the attack. Officers reportedly used pepper spray and other non-lethal projectiles to stop the fighting. Two inmates were taken to the hospital with what were described as non-life threatening injuries.
The California Men's Colony, which is located off Highway 1, houses approximately 4,000 minimum and medium custody inmates.