One inmate was killed and others were injured in a riot that erupted Sunday morning at the California Men's Colony prison northwest of San Luis Obispo, officials said.
The riot broke out shortly before 11 a.m. and involved more than 160 inmates at the medium-security yard in the East Facility, prison officials said. Guards intervened "immediately," shooting 40-millimeter rubber rounds and pepper spray to control the the crowd, officials said.
Multiple inmates sustained stab wounds, with nine taken to the hospital for treatment, authorities said. One of the nine, 25-year-old Matthew Cook, died of his injuries shortly after 1 p.m.
Cook was more than two years into a 13-year, eight-month sentence for several counts of first-degree burglary.
It's not clear what triggered the riot or whether authorities recovered any weapons. As of Sunday afternoon, authorities were still treating and rehousing inmates. No staff members were injured.
Officials will "go into investigative mode once we finish up," said Lt. Monica Ayon.
The prison, which was opened in 1954, houses 4,169 inmates.
Ayon said there was the potential Sunday for up to 600 inmates to be out on the yard.
"It is Sunday, so they're not at work, they're not at school. Everybody's on the yard," she said.