This the key and near-constant location in "Regrets". Pete and Myka are sent to investigate a rash of suicides at Riverton, and are informed by the Warden, Corinne Huggins, that some prisoners, including Reverend John Hill, blame the change of regime, since her predecessor was a strongly, overtly religious man.
The Riverton Maximum Security Prison is an incarceration facility constructed on top of an old quartz mine, and because of that the builders built the prison with quartz. As a result, people inside the building suffered hallucinogenic effects; most people saw visions of memories they were repressing. For example, a murderer thought he saw the people he had killed. These visions eventually drive people mad. Electrical storms that regularly ravaged the area were known to amplify the power of these visions, driving several people inside the prison into madness.These effects could be neutralized by Warden Matthew's Quartz Cross placed in the warden's office. The cross remains in Florida to this day.