Blood-soaked mattresses, singed bedding and abandoned medical supplies littered the campus of a Southern California prison Tuesday, a testament to the mayhem and violence of a weekend riot that shut down part of the institution and injured about 175 inmates, some critically.

Prison officials staged a tour of the devastation at the California Institution for Men in Chino to reveal the extent of the racially motivated riot that broke out Saturday evening and raged for four hours before guards could bring it under control.

Seven of the eight units in the prison's Reception Center West, one of several housing areas, were left uninhabitable, and more than 1,100 inmates have been moved to other facilities. One of the dorms was completely gutted by flames.

Eleven inmates remained hospitalized Tuesday, state prisons spokesman Terry Thornton said.

The area where the riot broke out was eerily empty and silent, with only a skeleton staff of corrections officers staffing checkpoints. A half-dozen officers scanned the exercise yard with metal detectors, searching for homemade weapons that inmates might have buried.

The riot began in a dorm during dinner hour and quickly spread, temporarily overwhelming staff, said Lt. Mark Hargrove, a prison spokesman.

Prisoners pried heavy metal grates from windows to escape and scrambled up and over the dorm roofs to get around 10-foot-tall hurricane fencing intended to keep them from the main exercise yard. The fence was installed after a previous riot in 2006.

"Hundreds were out of the units. Once they began rioting and breaking out, once they left, they created a situation where ... telling them to remain in the dorms was no longer in effect," Hargrove said. "They had decided not to follow that rule."

The prison was built in 1941 to house 3,000 inmates but held 5,900 men at the time of the riot. Each dorm holds 198 inmates and is assigned two guards, with a third guard who roams between every two dorms.

The prison serves as a reception and triage center for inmates from the four-counties around Los Angeles. About 95 percent of the prisoners are parole violators. Most are released or reassigned to another prison within 90 days, with exceptions for those who require special protection, such as sexual predators and gang dropouts.

The prison had been on a modified lockdown since Thursday after receiving reports that inmates were planning some violence, but none of the information indicated the problem would be in Reception Center West, Hargrove said.

Even in lockdown, the medium-security inmates can mingle freely in their dorms, where they are separated by race in two-man bunks. That puts men of different races in bunks next to each other, with just a few feet between them.

Outside the dorms, a narrow strip of grass separating the long, barracks-style housing units and an asphalt entrance area was still littered with debris. The chaotic tapestry featured discarded alcohol swabs, plastic handcuffs and latex medical gloves, filthy, bloodstained bedding and piles of abandoned clothes.

Two emergency plastic stretchers sat where they were left by paramedics who had treated inmates. One metal bunk had been ripped from its bolts and thrown into the yard.

An inmate had scrawled "8-08-09 HISTORY" on one mattress in black ink to mark the date of the riot.

Dominoes, cards, religious books, packs of crushed instant noodles and dozens of inmate identification cards fluttered in a warm breeze that still smelled of smoke next to the dorm gutted by fire.

Nearly every window was shattered inside the dorms that didn't burn. In one, the metal legs of a dismantled bunk had been used to pry large pieces of wood from the walls to use as weapons. Gang graffiti covered the beams and walls.

Amid the chaos, were signs of personal lives interrupted.

A black-and-white photo from an ultrasound of a fetus — age 21 weeks — lay at the foot of a bunk draped with a mattress coated in dried blood.

Next to bunk No. 193, a prisoner had left behind reminders of life on the outside: a magazine photo of a fawn standing in a snowy forest, pinned next to a religious card labeled "Path to Salvation."

By another bunk, an inmate had pinned a calendar with the days of August crossed out until the date of the riot.