On March 21, the California State Appeals Court, 4th district, division one, issued an opinion in Boydston v Padilla, D080921. It is 24 pages long and can be seen here. It says that independent voters have no constitutional right to vote in partisan presidential primaries. Some California parties do permit independent voters to vote in their presidential primaries, but others do not. Each party decides for itself before a presidential primary is held. The plaintiffs argued that independent voters must be permitted to vote in any party’s primary, regardless of that party’s wishes.
Generally the California Democratic Party permits independent voters to vote in its presidential primary, whereas the California Republican Party does not, although it did permit them to do so in 2004.