For being progressives, California has a states-right belief that really hasn't been seen in America since the South in 1860.  If it isn't in the US Constitution they think they can do it.

More rational people have believed that the Obama administration was not going to like any state circumventing U.S. law so when medical marijuana dispensaries were 'legalized' in California (medical marijuana itself was sort of legalized in the 1990s), the DEA busts began. Some municipalities defer to federal law and ban marijuana 'dispensaries' even while California claims they are legal.

Now, the California Supreme Court is set to settle the issue but it is basically a stall tactic to try and work out a compromise with the federal government so this does not end up in the real Supreme Court.  At stake is more than marijuana unless a decision were to be so properly worded as to defy belief.   If the Supreme Court agrees with California and states' rights are suddenly paramount over the federal kind, for example, Roe v Wade could be overturned.  The five largest states had their own abortion laws when the Supreme Court declared the federal government had the right to overrule the other 45 and make it legal everywhere, whether its citizens wanted it or not.

The logical and legal hurdle that has to be faced before then; state judges will try to rationalize how it is completely legal for California to have its own laws in defiance of the US government while contending local laws cannot defy the state ones.  Good luck with that.

A ban on medical marijuana dispensaries? Supreme Court to rule - LA Times