Blakely v. Washington, 542 U.S. 296 (2004), held that, in the context of mandatory sentencing guidelines under state law, the Sixth Amendment right to a jury trial prohibited judges from enhancing criminal sentences based on facts other than those decided by the jury or admitted by the defendant. The landmark nature of the case was alluded to by Justice Sandra Day O'Connor, who characterized the decision as a "Number 10 earthquake".