North Korea is at most in range of hitting the Aleutian Islands and blowing up a Russian Orthodox Church or two. Californy is a lot farther away than that.
As for missile defense, there is no such thing. The idea of missile defense is as cheesy a psychological trick as N Korea's nuke rattling is. The American PAC-3 are supposed to be able to intercept smaller missiles, and recently a missile on a stable, known course was shot down on the second attempt (the 1st one failed). But they are basically for show. They can't hit better than 1 out of 5 incoming, and probably worse than that.
Missile defense is basically an impossible technology. The problem is that an incoming missile is a large, high-speed rocket, especially ICBM's, which go through space at blazing speed. Once an ICBM starts falling back into the atmosphere, there is no way to intercept it. You can't fire up an ABM and hope that it will somehow get behind the ICBM and catch up, because it is climbing and the ICBM is diving. So you have to shoot for a head-on long shot. That means the steering on your ABM has to be able to have both incredible reaction time and incredible precision.
Building one requires cutting edge tech and lots of dollars. But defeating one is cheap and low-tech. Here are some easy ways to beat an ABM and to beat anti-missile lasers:
) put a cheap automated radar on the icbm, so it will disperse flares and chaff when it detects an abm
) make the icbm's flight wobble a bit, so that abm's can't predict their flight path
) cover the icbm with reflective or other protective material to protect it from lasers
) build 10 decoy icbm's for every 1 that has a warhead on it, to make the abm's get wasted. This is still much cheaper than abm tech.
If North Korea does eventually lob a missile at the US, it will probably hit, as long as they don't send a detailed flight plan to the US missile defense specialists so they can track and shoot it. A shot that long would be an icbm shot. No chance of hitting it.
But why worry so much about that? The Korean War never ended but the cease fire ended over 50 years ago. If their leaders were really madmen they would have broken it decades ago. They won't commit suicide.
If worst came to worst, they'd probably go for LA anyhow. Sorry but I won't miss LA if they do...
Again, missile defense is expensive and difficult - defeating missile defense is easy and cheap. Even if there's only one missile it's a long shot, especially if it's an ICBM, which is like trying to shoot down a falling meteor. Atmospheric missiles are a bit easier but the success rate is still low. Russia has already announced it will make cheap, easy missile-defense-defeating technology in retaliation for America's expensive program.>