The riot that ravaged a Southern California prison and injured 175 inmates began with a fight between black and Hispanic gang members, a stark reminder of the difficulty of race relations behind bars and the challenges of desegregating inmates.

In the nation's largest state prison system, black, Hispanic, Asian and white gangs generally don't mix. When they do, trouble typically follows.

"It isn't that everybody in the inmate population is against integration — they like their teeth," said David Miles, a 46-year-old black inmate at another prison, Sierra Conservation Center…

To be honest, it didn't look like racial segregation. I was standing among long rows of metal bunk beds in a room where 36 men of different races — black, white, Latino — live together more or less peaceably. But the setting was a dormitory for minimum-security inmates at the Sierra Conservation Center, a prison in Tuolumne County near Yosemite, and in such places, unwritten rules apply.

One of the rules is that each bunk must be shared by two men of the same race. The bunks are close together. A white inmate could probably shake hands with a black inmate in a neighboring bunk without either man having to get out of bed. But that's a horizontal matter. Vertically, prison politics require that each bunk be occupied by two men of one race. Beside someone of another race, yes. Above or beneath, no. I didn't ask about diagonal.

Well-meaning Americans have long debated how best to encourage racial integration. Should government be aggressive in bringing it about quickly? Or should we rely on social evolution to achieve it more slowly and organically?…

In what is being described as a major advancement for civil rights, California is ending a long-standing policy of segregation and allowing prisoners of different races to live together.

Despite its liberal reputation, California was among the few states that still used race as the determining factor for some male prisoners' cell assignments. Prison officials initially defended the measure as necessary to control racial and gang violence, but some inmates and civil rights activists disagreed.

The unwritten policy wound up before the United States' highest court in 2005. Starting this month, prison officials will begin fully integrating its cells, beginning with low-level offenders at two facilities…

When an inmate who is not black enters Will Williams' cell for the first time at San Quentin State Prison in Northern California, one of the last forms of legalized segregation will come to an end.

In a case that went as high as the U.S. Supreme Court, California's prisons must begin racially integrating their cells this month. Integration goes against an unwritten code of conduct among San Quentin inmates, which says they must never communicate with other races.

Inmates and guards admit they are nervous about the changes because so much of the violence inside the walls of the prison, which sits on the rocky shore of the San Francisco Bay, is caused by racial tensions…