Thanks for the link, it's interesting so I decided to take a look at the figures behind it on the
same site and I noted that Arkansas (looked at it because it's just above) showed a bigger decrease in crimes in half the categories than California did over the same time period - does that suggest that not having three strikes benefitted them? That's not entirely a serious question but it does make me consider whether there are wider social factors at work here, crime in general in America seems to have reduced over the same time period - while California may be impressive in this regard it's not entirely alone so I'd have to view the reduction in crime as hardly conclusive that it comes down to the three strikes rule alone.
Looking through some of the further pages suggests that California (and Arkansas) show higher drops than most but there's a fairly clear downward trend overall. If crime falls nationwide but maybe falls slightly more in one state then do you attribute it to a particular policy pursued or is it equally possible that it would have fallen as part of the nationwide drop anyway? And if you can grant the premise that it would likely have dropped regardless of policies pursued then you've got to question whether it might have fallen by a higher or lower amount than other states irrespective of a policy?