BLYTHE, Calif. (AP) — Eight corrections officers and an incarcerated man were injured in a riot involving around 200 inmates in the recreational yard of a Southern California prison, authorities said Thursday.

The violence erupted around 10 a.m. Wednesday as officers were escorting an inmate across the yard as part of a contraband investigation at Ironwood State Prison in Blythe, according to the California Department of Corrections and Rehabilitation.

The inmate headbutted a staff member, and as he was being subdued, “approximately 200 incarcerated people on the yard rushed toward the officers attacking them with fists and rocks,” the department said in a statement.

After deploying a rifle warning round, officers used “chemical agents and non-lethal impact rounds” to get the melee under control, the statement said.

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Eight staff members and one incarcerated person were treated at an outside hospital and later returned to the prison, officials said. The extent of their injuries wasn’t available.

So far, 30 incarcerated people have been identified as having direct involvement in the riot, and the investigation is ongoing.

Movement was restricted in yards and dayrooms at all prisons statewide for 24 hours as officials conducted a routine threat assessment.

Ironwood, a minimum-medium security facility in the desert east of Los Angeles, opened in 1994 and houses about 2,500 male inmates.

Inmates across California are being confined to their cells after a major riot involving an estimated 200 incarcerated people left eight staff members and one prisoner with serious injuries, authorities said.

The Jan. 31 riot at Ironwood State Prison in the Riverside County city of Blythe started when an estimated 200 prisoners rushed corrections officers, attacking them with fists and rocks. During the fracas, officers say they fired a “warning shot,” and deployed tear gas and “non-lethal impact rounds” at the inmates. Eight prison staff members and one incarcerated person were hospitalized with injuries, and later released.

The incident prompted a statewide threat assessment, meaning that prisoners across the state are being restricted to their cells, authorities said. The threat assessment is supposed to last only 24 hours, according to a statement by the California Department of Corrections and Rehabilitation.

The riot began around 10 a.m. when an incarcerated man head-butted a corrections officers who had detained him as part of a contraband investigation. The head butting — which occurred as staffers were escorting the man across a prison yard — prompted 200 inmates to attack the officers.

Authorities say they’ve identified 30 suspects and are still investigating the incident. The state Office of the Inspector General was also notified.

The past few months have been a particularly violent time for California prisons, including a recent sexual assault of a staffer at Sierra Conservation Center in Jamestown and a number of homicides across the state. Many of the killings have been attributed to problems within the Mexican Mafia prison gang and its subsidiaries in the wake of the July 2023 fatal stabbing of a member named Michael “Mosca” Torres, who was at California State Prison, Sacramento, awaiting trial in a federal racketeering case.