California has sentenced 900 people to death since 1978 when it reintroduced the death penalty, but has executed just 13, the last in 2006. Seven people have died of other causes while on death row for each person who was executed. The appellate process takes twenty-five years on average (twice the national average), in addition to the often lengthy process of convicting someone of the death penalty in the first place.
A federal judge held today that the entire process is unconstitutional because the ultimate reality that chooses which unlucky few people will be executed and who will not is so arbitrary and capricious that it violates the 8th Amendment prohibition against cruel and unusual punishment.
If the ruling sticks is will remove 742 people from death row, more than any court ruling in the history of the United States other than the ruling of the U.S. Supreme Court in 1972 that temporarily ended the death penalty in the United States. Nationwide there are 3,070 inmates in the United States who have been sentenced to death and have not had those sentences reversed on appeal. Almost a quarter of them could potentially have death sentences converted into life in prison by this ruling.
An appeal, if the State of California chooses to pursue it, would be to the United States Court of Appeals for 9th Circuit (arguably the most liberal federal appeals court in the country on death penalty issues), and then to the U.S. Supreme Court. The state attorney general could, however, simply decline to appeal the case and end the death penalty in California, as was done in the case of Proposition 8, a plausible result giving the officials who hold those offices. Kamala Harris, the attorney general, is a leading opponent of capital punishment and Governor Brown isn't a strong supporter of it either. A 2012 referendum to abolish the death penalty in California narrowly failed with 48% of voters supporting the measure.