Despite vast expenditures on U.S. prison construction in the late twentieth century, infrastructure has not kept pace with the punishment imperatives of mass incarceration. Dangerously overcrowded confinement conditions remain widespread in prisons and jails, raising recurring dilemmas about the judicial oversight, and legal regulation of correctional policy. Perhaps no state better exemplifies the prison overcrowding crisis than California, which operates one of the nation's and western world's largest prison systems. After several decades of rapid growth, by 2011 the state incarcerated nearly twice the number of people its prisons were designed to hold. Despite these levels, California's recidivism rate remained one of the highest in the nation; roughly 60 percent of those released from prison reoffended within three years (Pew Center on the States 2011). Such extreme prison overcrowding combined with its lack of crime control efficacy led to historic intervention by the U.S. Supreme Court in Brown v. Plata (2011). In a 5-4 decision, the Plata court found California's conditions of confinement to violate the Eighth Amendment's prohibition on cruel and unusual punishment and ordered the state to reduce its prison population to 137.5 percent of capacity (or, by roughly 40,000 people) within two years. Justice Scalia decried the order as "the most radical injunction issued by a court in our Nation's history" (Brown v. Plata 2011: 1 of Scalia dissent).Brown v. Plata has understandably been characterized as a "remarkable" case (Simon 2014). Even more remarkable is the state of California's response. While states have often sought to comply with population cap orders by expanding prison capacity (e.g., Feeley and Rubin 1998; Guetzkow and Schoon 2015; Schoenfeld 2010), California enacted legislation known as "Public Safety Realignment," or Assembly Bill 109 (AB 109 2011), which localized the onus of compliance to individual counties (Schlanger 2013). AB 109 devolves the supervision of most nonviolent offenders to the county level and, notably, delegates unprecedented discretion to local practitioners to either incarcerate those previously sent to state prison in local jails or to use alternative, community-based sanctions that do not entail incarceration (Pen. Code §1170(h); §17.5). California's unique response, thus, raises the possibility of decarceration-rather than prison expansion- as a viable mode of legal compliance with court intervention for the first time in decades.In a keynote address to the National Institute of Justice, criminologist Joan Petersilia (2012) said this about California's Realignment: "It is the biggest criminal justice experiment ever conducted in America, and most people don't even know it's happening." The Economist (May 19, 2012) has also called AB 109 "one of the great experiments in American incarceration policy," in part due to concerns about its effects on future crime levels, but also because whether it will in fact lead to decarceration, as many reformers have hoped (e.g., ACLU 2012), remains an open question. Emerging awareness of the underlying variation in California counties' historical reliance on the state prison system has raised concerns that the relatively small number of historically high prison using counties-counties that disproportionately drove the state's prison overcrowding crisis in the first place (e.g., Ball 2012)-will use the discretion afforded to them under Realignment to either subvert the law's central mandates or to simply relocate the sites of incarceration from state prison cells to local jail cells (Lynch 2013; Petersilia and Snyder 2013).Realignment's "experiment" has attracted interest from public policy scholars (e.g., Bird and Grattet 2014; Lofstrom and Raphael 2013; Males and Goldstein 2014) and legal scholars (e.g., Ball 2012; Schlanger 2013; Zimring 2014). However, this is the first study to empirically address the sociolegal questions raised by this distinctive form of regulation, which renders legal compliance possible because of-not despite-local variations in front-line implementation. …