That's a pretty big state with a lot of delegates.
"California currently has a "modified" closed primary system. SB 28 (Ch. 898, Stats. 2000), relating to primary elections, was chaptered on September 29, 2000 and took effect on January 1, 2001. SB 28 implemented a "modified" closed primary system that permits unaffiliated ("decline to state") voters to participate in a primary election if authorized by an individual party's rules and duly noticed by the Secretary of State.
(Ch. 898, Stats. 2000)"
http://www.sos.ca.gov/elections/elections_decline.htmIt is really complicated, state by state ... because there are open, semi-open, closed, and semi-closed primaries: whether unaffiliated/independent voters can participate, and the rules for doing so, varies widely.
In general, an "open" primary means that voters of ANY party can vote in any primary (i.e., Republicans could vote in the Democratic primary). Many states have something between that: independents can choose where to vote, but people may not switch parties to vote in the other's primary. Some states, such as Illinois, require that you vote in the same primary you voted in the previous election (though I don't think it is effectively enforced). But there is no doubt that independent voters can play crucial roles in primaries. I, myself, am opposed to truly open primaries: I don't like the idea of the other party crossing over to interfere. But I'm divided over the issue of independents voting. In theory, I'd prefer that people register to be Democrats, to build party strength. But in reality, today a lot of people do not want to register in one party or another and prefer to remain unafilliated, though they may vote one party more than another. That's a currently reality ... it's up to the parties to lobby if they want to change rules in individual states.