A. An easy -- and free -- place to start is the Online Archive of California. A quick search of the catalog for prison reveals a range of materials, including California State Prison at San Quentin records, 1851-1910, San Quentin Folsom Prison Index 1910, and even a reward poster for escapees from Folsom in 1890. Only a few of these collections are online, but this statewide catalog can direct you to the repository holding the actual records, such as the state library or historical society.

If your criminal ancestor was incarcerated in a federal, rather than a state, prison, the records would be housed (along with federal court files, which may be helpful) at the National Archives and Records Adminstration (NARA) regional offices. Alcatraz records, for example, are at the NARA branch in San Francisco; you'll find a roster of former inmates, 1934 to 1963, NARA's website.