California officials frequently cite possession of black literature, left-wing materials, and writing about prisoner rights as evidence of gang affiliation. In the dozens of cases I reviewed, gang investigators have used the term "[BGF] training material" to refer to publications by California Prison Focus, a group that advocates the abolition of the SHUs; Jackson's once best-selling Soledad Brother; a pamphlet said to reference "Revolutionary Black Nationalism, The Black Internationalist Party, Marx, and Lenin"; and a pamphlet titled "The Black People's Prison Survival Guide." This last one advises inmates to read books, keep a dictionary handy, practice yoga, avoid watching too much television, and stay away from "leaders of gangs."

The list goes on. Other materials considered evidence of gang involvement have included writings by Mumia Abu-Jamal; The Black Panther Party: Reconsidered, a collection of academic essays by University of Cincinnati professor Charles Jones; pictures of Assata Shakur, Malcolm X, George Jackson, and Nat Turner; and virtually anything using the term "New Afrikan." At least one validation besides Pennington's referenced handwritten pages of "Afro centric ideology."

As warden of San Quentin Prison in the 1980s, Daniel Vasquez oversaw what was then the country's largest SHU. He's now a corrections consultant and has testified on behalf of inmates seeking to reverse their validations. As we sat in his suburban Bay Area home, he told me it is "very common" for African American prisoners who display leadership qualities or radical political views to end up in the SHU. Similarly, he recalls, "we were told that when an African American inmate identified as being Muslim, we were supposed to watch them carefully and get their names."