Urban Institute, Justice Reinvestment Initiative State Assessment Report (2014).
Drug Policy Alliance, Marijuana Arrests in Colorado After the Passage of Amendment 64 (2014).
Justice Reinvestment Initiative Resources (excellent listing of every state with JRI's, reports, and information, and lots of other information and reports).
The above link has plenty of state materials, but there may be others out there. Most information and Acts appear easily attainable through simple google searching, e.g. see this one for Nebraska.