In the prison parts of the movie, Olmos managed to get on screen real-life gang members from the Bloods and Crips, Aryan Brotherhood, Nazi Lowriders, Hell's Angels, 18th Street, White Fence, La Colonia de Watts, Dogtown, East Side Clover and the infamous Black Guerilla Family.
Most of the extras who were dressed as prisoners quit after the first day of filming. They were kept in a gated area next to an open sewer and had to ask guards to use the bathroom. Guards are used to ignoring prisoners, so they mostly ignored extras dressed as prisoners. They weren't given enough water and lunch wasn't served until late in the day. Conditions slightly improved on the second day, but on the third and final day of filming at Folsom Prison there were about 25 of the 200 that showed up on the first day.
When the Mexican inmates are walking up with the mop and bucket to assassinate the African-American inmate, it shows the African-American inmate laying in just a t-shirt on his bed and in the next scene after hes caught on fire he's wearing his long sleeve button up.
J.D.: If we show weakness now, homes, everybody's gonna see it not just the mayates and wops as La Nuestra Familia as well. They're just waiting to make their fucking move. This way we can do it clean. Do what Scagnelli did, form them shoot out.
Young Montoya Santana: [Mundo is being devoted into the gang]
Come on, give me your hand. You know what, ese, White Fence, Maravilla, Lomita, they've been around here longer than us, you know. It's cool. We've got our own clika, strong clika. Finally getting into our own, gaining respect.