San Luis Obispo – More than 160 inmates were involved in a large-scale riot in the East Facility medium-custody yard at California Men’s Colony (CMC) Sunday morning, that left one inmate dead and several others injured.

CMC staff responded immediately, utilizing force consisting of 40 mm less-than-lethal direct impact rounds and chemical agents to gain control of the incident. No deadly force was used, and no staff members were injured.

Multiple inmates received stab wounds, with nine being transported to an outside hospital for further treatment. According to Sierra Vista Regional Medical Center spokesman Ron Yukelson, the hospital was notified of a “mass casualty incident” about noon. The hospital had received two trauma patients and seven patients with less-serious injuries.

One of the nine, Matthew Cook, was pronounced dead at 1:05 p.m. Cook, 25, was received by CDCR in April 2015 from San Joaquin County with a 13-year, 8-month sentence for several counts of burglary in the first degree. Cook’s next-of-kin has been notified.

The riot started in the prison yard at Facility A and involved a large number of inmates. The cause of the riot is unknown, and inmate movement has been limited to facilitate the investigation into this matter.

CMC was opened in 1954 and houses 4,169 inmates. The prison’s primary mission is to provide secure housing for minimum and medium security inmates, as well as programming opportunities for self-improvement.